NSC800 Conversion: Difference between revisions

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Work in progress!


[[Image:NSC800.png||center]]<br/>


Protytype!
[[Image:NSC800.jpg]]
Current version!  (courtesy John Wiggins)
[[Image:NSC800_1.jpg]]


== What is this all about? ==
== What is this all about? ==


External serial bidirectional communication on the Model 100 today is limited to (1) the RS-232 port and (2) the modem port, both of which use the single UART in the computer.
Motivated by 2 things
* discovery (to me) of the NSC800 Z80 processor that is 80C85 like
* continuing to work in the direction of CP/M
 
I have invested some time and effort in developing a conversion that supports NSC800 operation in the M100, both for standard BASIC use, as well as CP/M (in conjunction with REXCPM).  Partly this has been motivated simply by curiosity.  However, in CP/M it actually broadens the software applicability since quite a bit of CP/M software is Z80.
 
If you have an interested in doing this conversion please get in touch with me at Twospruces at --the google mail service.
 
 
== What are the tradeoffs? ==
 
When installed, you get an M100 that is ALMOST exactly the same.  Differences:
  1.  Z80 not 80C85...ok
  2.  Still runs the same BASIC applications
  3.  Cassette port no longer works as the 80C85 uniquely has the SID/SOD pins but NSC800 does not.
  4.  NSC800 is NOT COMPATIBLE with REXMGR software, so you can't benefit from the standard REX features when using NSC800.
  5.  almost 100% compatible with M100 software, even machine code.  Except for:
      *  anything that makes use of the hardware interrupts - Timer, RS-232, BCR port - may require a patch to work.
  6.  When combined with REXCPM, you get to run Z80 software in M100 CP/M!  See below section on M100 CP/M use.
 
The NSC800 processor uses the interrupts in a slightly different way, so machine code that uses the interrupts needs to change a bit.
Patches need to be applied to the M100 Main ROM (see below) to tweak things a bit to work.
 
== Required Changes ==
 
There are 2 areas of change that are needed.
Firstly you have to adapt the NSC800 to the 80C85 socket.  There are a couple of tradeoffs to make. 
Secondly, the NSC800 needs to use a slightly different Main ROM.
 
To get started on this project, one can leverage the work done in the past.  In fact an NSC800 conversion for 80C85 was posted back in the early 80s for S100 computers equipped with an 8080/8085 processor board.  The information is posted below, from
Microsystems September 1984.
 
[[Media:NSC800 conversion1.JPG|NSC800 conversion1.JPG]]
 
[[Media:NSC800 conversion2.JPG|NSC800 conversion2.JPG]]
 
This article lists considerations; from my work in M100 the things that any adapter has to deal with are listed below.
 
  1.  Inversion of the interrupt signals
  2.  Conversion of the 50/50 duty cycle RST7.5 signal to a 100 usec low pulse (NSC800 is level triggered not edge).
  3.  4.9152 MHZ clock generation circuitry.
  4.  And in the case of a dual processor conversion, certain NSC800 signals are not tri-state in RESET.
 
Note:  it seems that the M100 RAM/ROM and REX are all tolerant of the short opcode fetch read/write cycle.  So, no wait state generator appears to be needed.
 
A single NSC800 CPU conversion is what is available today.  I am working on a dual CPU conversion as well.
 
The single NSC800 conversion design has gone through 4 revisions and is now at V5.
  * designed for 5MHz operation
  * assumes REXCPM is providing all SRAM needed (so the RAM is fast enough)
  * assumes there is a suitably fast M100 patched main ROM installed
  * can be configured to run at 2.5MHz if required
 
== 1CPU NSC800 conversion PCB ==
 
The V5 schematic is here.
 
[[Image:NSC800_V5.PNG|NSC800_V5.PNG]]
 
PCB images are below.
 
[[Image:NSC800_V5_pri.PNG|NSC800_V5_pri.PNG]]
 
 
[[Image:NSC800_V5_sec.PNG|NSC800_V5_sec.PNG]]
 
== Modified M100 Main ROM ==
 
As mentioned, since the interrupt control mechanisms in NSC800 are slightly different, the M100 main ROM needs to be patched to support NSC800.
 
The NSC800 patch needs extra code space to be created in the ROM.  To do that, an original patch has been verified that creates a block of unused space in the main ROM as published by Microsoft.
 
[[Media:base_patch.zip|base_patch.zip]]
 
Once this base patch is applied to the ROM, you have space now for the next set of patches, here.
 
 
[[Media:patch_nsc800.zip|patch_nsc800.zip]]
 
 
All these patches rolled up into a binary:  (here I used the T102 base ROM as the starting point)
 
[[Media:M102_nsc800.zip|M102_nsc800.zip]]
 
 
These are what I use today.  If I find bugs I will post updates.
 
 
 
 
== Notes on use with M100 CP/M ==
 
Probably, you have installed an NSC800 processor and supporting M100/T102 main ROM, so that you can use M100 CP/M and gain the benefit of Z80.
I suppose to be fair it is possible to run the NSC800 in the laptop, and yes it would be a Z80 - so you could write new programs that are based on Z80 opcodes.  Not sure that would be worth it. 
 
So, how does one get M100 CP/M rolling with the NSC800?
CP/M 2.2 is generally based on 8080, so the operating system itself is fine.
Well you for sure need a REXCPM, either 2MB or 4MB.
I will assume that you would have already been familiar with setting up M100 CP/M using the standard config with 80C85 installed.
 
There are a few major considerations.


This hack enables the BCR port to send and receive half duplex serial TTL signals.  The BCR port is already set up for TTL receive function as this is used for the Bar Code Reader function.  So this hack provides facility to transmit as well.  In addition I provide some software routines that demonstrate the capability.
  1.  RXCMGR software does NOT support NSC800!  RXCMGR makes extensive use of the 80C85 undocumented opcodes, so it won't run on NSC800.
  2.  Installing and running CP/M relies solely on the tools provided for M100 CP/M.
  3.  In order to load up the M100 CP/M utilities, you will need a DOS of some kind.  See below.
  4.  M100 CP/M, as it comes in standard form, IS generally compatible with NSC800. 
  5.  IMPORT and EXPORT are not written using 8080 opcodes, so you will need replacements.  See below.
  6.  If you want to use the BCR Hack for external video over MVT100, you need to (1) change the hack slightly and (2) patch CP/M.  See below.
  7.  Also note - the utilities for backup/restore of REXCPM also do not work on NSC800.


BCR port serial TTL is supported in Model 100 CP/M as well as with the VT100 Driver, for use with VT100 Terminal or other VT100 CRT solution.


Get in touch with me at Twospruces at --the google mail service.


== Acknowledgements ==
=== How do I transfer files into the laptop? ===


I would like to acknowledge and thank those that have contributed to the project:
TELCOM application in M100 still works with M100.  So, any .DO file is loadable using the standard methods with TELCOM.


'''Philip Avery''' - for efforts with CP/M and attached Video using the VT100 Adapter
  But why?  What about the interrupt issue? 
  ... in the modified T102 main rom, I have patched it up so that the serial port still works correctly.
  The T102 main rom provides routines for getting and sending data over RS-232 and those routines work fine.
  However, any serial port software that uses POLL MODE will not work correctly as the NSC800 does not have an opcode like SIM/RIM.
  --> so as a general rule I would say - assume that serial port and BCR port work fine with NSC800, but it is possible that 3rd party software
  might try to POLL the interrupt status and that could cause a problem.  Try first, and decide.




==Improved BCR Hack==
==== NTEENY for M100 mode ====
TELCOM alone does not solve the problem, since .CO and .BA programs are not text.  What to do?
Well, what about TEENY?  TEENY happens to make use of SIM opcode unfortunately. 
So, I have built on the great work of Ron Wiesen, and modified TEENY to run on NSC800.


===CP/M Status===
I have been using NTEENY below and do not observe any problems, but please do report back if you find any issues.
* currently supported in CPM210/410 as CASS video option
This is for NSC800 only, please use standard TEENY on 80C85.


=== Supported Models ===
*  TRS-80 Model 100
*  a hardware hack for T102 is likely however not explored at this time
*  a similar hack should be possible for all ModelT versions.


=== The Hardware Modification ===


=== The Software ===
Version 1 loads and runs NTEENY directly.  Get the CO via SAVEM"NTEENY.CO",62213,62960,62213


[[Media:nteeny.zip|nteeny.zip]]






Version 2 creates NTEENY.CO


[[Media:nteeny_v2.zip|nteeny_v2.zip]]


==Original BCR Hack==
This is not as fancy as Ron's because it loads and runs at a fixed location 62213, but it should suffice.


===CP/M Status===
==== TPDD Utilities for CP/M mode ====
* currently supported in CPM210/410 as CASS video option


=== Supported Models ===
*  TRS-80 Model 100
*  a hardware hack for T102 is likely however not explored at this time
*  a similar hack should be possible for all ModelT versions.


I wrote some CP/M utilities for directly accessing a TPDD (like an actual TPDD, or LaddieAlpha) from CP/M.
These programs assume files are named with 8.3 format in both the TPDD and of course CP/M.




=== The Hardware Modification ===
[[Media:TPDD_utils.zip|TPDD_utils.zip]]


'''UDPATE:  an improved implementation is being tested, which is more universal.  SOD pin is available on 80C85 but not Z80.  As such, there is a change where we can utilize /Y1 signal...making this hack accessible with both NSC800 and 80C85. '''
  TD.COM:  TPDD directory
  TS.COM:  Save file to TPDD
  TL.COM:  Load file from TPDD
  TK.COM: Kill file on TPDD
  (soon to come:  TCD.COM: TPDD change directory)




The core of the modification is to connect pin 3 of the BCR port to the SOD output of the CPU. This is accomplished by adding a single wire to the PCB.
Transfer these programs using IMP80 (and change .COM to .CO for transfer) into CP/M.


  This page details the hardware change required to transmit at 57600 baud with minimal changes.
=== How do I get M100 CP/M loaded up? ===
  It can be demonstrated that, in the M100, both serial Tx and Rx is possible at 57600 over the BCR port.


  Tx and Rx at higher speeds is more challenging.  Tx speeds of up to 128000 baud have been demonstrated.
The best way to get M100 CP/M running with NSC800 is to start with a known good M100 CP/M installation, and then convert the hardware.
  Transmission at this rate requires disconnection of the cassette port Tx filter at C63.
  If you remove C63 you get better signal quality for TTL serial, but the cassette port is no longer usable.
  If, like me, you never use the cassette port they it may not be a big deal.


The following image shows the modification to the M100 Cassette/BCR port circuitry.
The currently posted version of M100 CP/M happens to use 8085 undocumented opcodes.  A modified version of M100 CP/M has been prepared that is pure 8080.


[[Image:ckt2.png||center]]<br/>
[[Media:CPM440_patched.ZIP|CPM440_patched.ZIP]]


Here we see a strap added from pin 12 of M34 to pin 3 of the BCR port, defining this pin as Tx data.


The following image shows the placement of the strap on the secondary side of the M100 PCB.
  This version of M100 CP/M includes the following changes
  1. all 8085 undoc opcodes have been removed, and the code reworked.
  2. a patch has been applied to support the NSC800 version of the BCR hack.


Because stock IMPORT/EXPORT don't work with the NSC800, that problem needs to be solved BEFORE you install the NSC800 CPU.


[[Image:layout2.png||center]]<br/>
I modified Philip's IMPORT and EXPORT routines to eliminate the 80C85 undoc opcodes and SIM/RIM.
The result are 8080 based versions called IMP80 and EXP80, below.


=== The Software ===
[[Media:8080_import_export.zip|8080_import_export.zip]]


As mentioned, the use of the BCR port to send TTL data to the external CRT is supported in Model 100 CP/M, as well as by using the VT100 Driver, which integrates the external CRT with BASIC, based on Microsoft Disk BASIC for the Model 100.


Additionally, I include some code here as examples.
Steps to get M100 CP/M and NSC800 running:


==== 57600 Baud Routines ====
  0.  Modify the M100 to put a socket in place where the 80C85 is.  Install the 80C85 for now.
  1.  Start with a freshly installed REXCPM in an M100, with no CP/M installed.  So, a blank REXCPM.
  2.  Follow Philip's procedures to get an initial M100 CP/M system up and running.  Use the posted files.
  3.  Run M100 CP/M from the laptop LCD, not RS-232 or CASS (BCR).
  4.  Using IMPORT, transfer into CP/M the modified IMP80 and EXP80.  Test that they work as expected.
  5.  Update M100 CP/M to use CPM440_patched.bs, by using CPMUPD.CO.  Change the filename to CPM440.bs.
      Switch back to M100 mode.  Run the command CPMUPD.CO CPM440.bs
      This will update the CP/M operating system.


Currently both CP/M and my own VT100 driver user 57600, using the modification posted here.
OK, now you have a system ready to transplant the NSC800.  Next..


The following code can be compiled, and run in Model 100 to demonstrate transmission between 2 machines at 57600.
  6.  Open the M100, and install (1) the NSC800 and (2) the modified main ROM.
  7.  Close up the laptop, and power up.  You should see that the NSC800 is working.
  8.  Now, start CP/M and you should be up and running.


Tx routine:
    [[Media:keysnd_57600.zip|keysnd_57600.asm]]
Rx routine:
    [[Media:bcrx_57600.zip|bcrx_57600.asm]]


Since the NSC800 and RXCMGR are incompatible, use CPM.CO to start CP/M.


I may have done the M100 <--> M100 testing using an improved circuit (IE remove C63). I'm not sure; if you do try this experiment keep it in mind that the Tx signal quality is better if you pull C63. This of course makes the cassette port useless.
For added convenience, I have made a version of CPM.CO as a .DO file, for easy file transfer to the laptop.
Use this if your CPM.CO file gets corrupted.


==== Higher speed Tx Routines ====
[[Media:CPM_DO.ZIP|CPM_DO.ZIP]]


Faster transmission is possible; both 115600 and 128000 baud have been demonstrated.  The core Tx routines are provided here.
Comments welcome on this procedure!


for Tx at 57600 baud:
=== What about using the BCR Hack for external video? ===
    [[Media:bcrtx_57600.zip|bcrtx_57600.asm]]
for Tx at 115600 baud:
    [[Media:bcrtx_115600.zip|bcrtx_115600.asm]]
for Tx at 128000 baud:
    [[Media:bcrtx_128000.zip|bcrtx_128000.asm]]


Ah, great question!  As you know M100 CP/M supports 3 types of video


  1.  M100 native LCD
  2.  VT100 video over RS-232
  3.  VT100 video over (a suitably modified) BCR port


==== Timing for 57600 Baud ====
With NSC800 processor, since we don't have the SID or SOD pins nor the RIM/SIM opcodes, the BCR hack needed to change.
That change is documented here:


Since the processor is 100% busy reading in bits during Rx functions, the requirement for the BCR port receiver is to read and place the byte into memory before the stop bit is completed.  The faster the Rx can process the received byte, the faster the link rate can be.  At 57600 baud that is about 17 microseconds.  Typical processor instruction time is between 1.2 and 1.6 microseconds, so this is about 10-12 instructions max (42.65 clock cycles).
https://bitchin100.com/wiki/index.php?title=BCR_TTL_SERIAL_HACK#NSC800_BCR_Hack
I think that is enough time to write to memory and increment a counter or a parity, and a jump or 2.
57600 baud then looks feasible, even for large memory transfers so long as the buffer can be continuously written to without interruption while the PC is sending data. It also means that the RS-232 port could run flat-out at 5.7 kBytes/sec in the Rx direction.
In the Tx direction it similar, but it takes a small amount of time to prepare the data before sending the start bit and following data bits.  I think it is probably better than 5.5 kbytes/sec.


For CP/M and REXCPM backup/restore this means
The original hack "V1" uses the SOD pin... not good for NSC800.
  4MB backup restore time could be about 12 minutes @57600 baud
A more generic hack "V2" uses the Motor on/off relay control to bit bang the Tx serial data at high speed.
    -- assuming "large packet support" on LaddieAlpha, and direct writes to block RAM.
V2 works for both 80C85 and NSC800.


This change requires a bit of software change to work, though.
To make M100 CP/M send video data over this modified BCR hack, a patch is needed.


What about 115600 or 128000 baud?  While the Tx side has been shown to work, the Rx side is the challenge.
The patched CPM440.bs file posted above includes this patch.
Challenge 1.  The M100 ROM requires an initial interrupt and then 3 jumps to get to the RST6.5 hook.  The M100 has to make it to the RX code before the data arrives.  This places a practical limit of 57600 on the rate.  76800 is too fast. However if an option ROM was used this could potentially be sped up.


A quick look at BCRX.ASM above suggests the RX bit reception time could be reduced to 29 clock cycles, supporting ~85000 baud.




Latest revision as of 05:41, 5 May 2024


Protytype!

NSC800.jpg

Current version! (courtesy John Wiggins)

NSC800 1.jpg

What is this all about?

Motivated by 2 things

  • discovery (to me) of the NSC800 Z80 processor that is 80C85 like
  • continuing to work in the direction of CP/M

I have invested some time and effort in developing a conversion that supports NSC800 operation in the M100, both for standard BASIC use, as well as CP/M (in conjunction with REXCPM). Partly this has been motivated simply by curiosity. However, in CP/M it actually broadens the software applicability since quite a bit of CP/M software is Z80.

If you have an interested in doing this conversion please get in touch with me at Twospruces at --the google mail service.


What are the tradeoffs?

When installed, you get an M100 that is ALMOST exactly the same. Differences: 

  1.  Z80 not 80C85...ok
  2.  Still runs the same BASIC applications 
  3.  Cassette port no longer works as the 80C85 uniquely has the SID/SOD pins but NSC800 does not.
  4.  NSC800 is NOT COMPATIBLE with REXMGR software, so you can't benefit from the standard REX features when using NSC800.
  5.  almost 100% compatible with M100 software, even machine code.  Except for:
      *  anything that makes use of the hardware interrupts - Timer, RS-232, BCR port - may require a patch to work.
  6.  When combined with REXCPM, you get to run Z80 software in M100 CP/M!  See below section on M100 CP/M use.

The NSC800 processor uses the interrupts in a slightly different way, so machine code that uses the interrupts needs to change a bit. Patches need to be applied to the M100 Main ROM (see below) to tweak things a bit to work.

Required Changes

There are 2 areas of change that are needed. Firstly you have to adapt the NSC800 to the 80C85 socket. There are a couple of tradeoffs to make. Secondly, the NSC800 needs to use a slightly different Main ROM.

To get started on this project, one can leverage the work done in the past. In fact an NSC800 conversion for 80C85 was posted back in the early 80s for S100 computers equipped with an 8080/8085 processor board. The information is posted below, from Microsystems September 1984.

NSC800 conversion1.JPG

NSC800 conversion2.JPG

This article lists considerations; from my work in M100 the things that any adapter has to deal with are listed below. 

  1.  Inversion of the interrupt signals
  2.  Conversion of the 50/50 duty cycle RST7.5 signal to a 100 usec low pulse (NSC800 is level triggered not edge).
  3.  4.9152 MHZ clock generation circuitry.
  4.  And in the case of a dual processor conversion, certain NSC800 signals are not tri-state in RESET.

Note: it seems that the M100 RAM/ROM and REX are all tolerant of the short opcode fetch read/write cycle. So, no wait state generator appears to be needed.

A single NSC800 CPU conversion is what is available today. I am working on a dual CPU conversion as well.

The single NSC800 conversion design has gone through 4 revisions and is now at V5. 

  * designed for 5MHz operation
  * assumes REXCPM is providing all SRAM needed (so the RAM is fast enough)
  * assumes there is a suitably fast M100 patched main ROM installed
  * can be configured to run at 2.5MHz if required

1CPU NSC800 conversion PCB

The V5 schematic is here.

NSC800_V5.PNG

PCB images are below.

NSC800_V5_pri.PNG


NSC800_V5_sec.PNG

Modified M100 Main ROM

As mentioned, since the interrupt control mechanisms in NSC800 are slightly different, the M100 main ROM needs to be patched to support NSC800.

The NSC800 patch needs extra code space to be created in the ROM. To do that, an original patch has been verified that creates a block of unused space in the main ROM as published by Microsoft.

base_patch.zip

Once this base patch is applied to the ROM, you have space now for the next set of patches, here.


patch_nsc800.zip


All these patches rolled up into a binary: (here I used the T102 base ROM as the starting point)

M102_nsc800.zip


These are what I use today. If I find bugs I will post updates.



Notes on use with M100 CP/M

Probably, you have installed an NSC800 processor and supporting M100/T102 main ROM, so that you can use M100 CP/M and gain the benefit of Z80. I suppose to be fair it is possible to run the NSC800 in the laptop, and yes it would be a Z80 - so you could write new programs that are based on Z80 opcodes. Not sure that would be worth it.

So, how does one get M100 CP/M rolling with the NSC800? CP/M 2.2 is generally based on 8080, so the operating system itself is fine. Well you for sure need a REXCPM, either 2MB or 4MB. I will assume that you would have already been familiar with setting up M100 CP/M using the standard config with 80C85 installed.

There are a few major considerations. 

  1.  RXCMGR software does NOT support NSC800!  RXCMGR makes extensive use of the 80C85 undocumented opcodes, so it won't run on NSC800.
  2.  Installing and running CP/M relies solely on the tools provided for M100 CP/M.
  3.  In order to load up the M100 CP/M utilities, you will need a DOS of some kind.  See below.
  4.  M100 CP/M, as it comes in standard form, IS generally compatible with NSC800.  
  5.  IMPORT and EXPORT are not written using 8080 opcodes, so you will need replacements.  See below.
  6.  If you want to use the BCR Hack for external video over MVT100, you need to (1) change the hack slightly and (2) patch CP/M.  See below.
  7.  Also note - the utilities for backup/restore of REXCPM also do not work on NSC800.


How do I transfer files into the laptop?

TELCOM application in M100 still works with M100. So, any .DO file is loadable using the standard methods with TELCOM. 

  But why?  What about the interrupt issue?  
  ... in the modified T102 main rom, I have patched it up so that the serial port still works correctly.
  The T102 main rom provides routines for getting and sending data over RS-232 and those routines work fine.
  However, any serial port software that uses POLL MODE will not work correctly as the NSC800 does not have an opcode like SIM/RIM.
  --> so as a general rule I would say - assume that serial port and BCR port work fine with NSC800, but it is possible that 3rd party software
  might try to POLL the interrupt status and that could cause a problem.  Try first, and decide.


NTEENY for M100 mode

TELCOM alone does not solve the problem, since .CO and .BA programs are not text. What to do? Well, what about TEENY? TEENY happens to make use of SIM opcode unfortunately. So, I have built on the great work of Ron Wiesen, and modified TEENY to run on NSC800.

I have been using NTEENY below and do not observe any problems, but please do report back if you find any issues. This is for NSC800 only, please use standard TEENY on 80C85.


Version 1 loads and runs NTEENY directly. Get the CO via SAVEM"NTEENY.CO",62213,62960,62213

nteeny.zip


Version 2 creates NTEENY.CO

nteeny_v2.zip

This is not as fancy as Ron's because it loads and runs at a fixed location 62213, but it should suffice.

TPDD Utilities for CP/M mode

I wrote some CP/M utilities for directly accessing a TPDD (like an actual TPDD, or LaddieAlpha) from CP/M. These programs assume files are named with 8.3 format in both the TPDD and of course CP/M.


TPDD_utils.zip 

  TD.COM:  TPDD directory
  TS.COM:  Save file to TPDD
  TL.COM:  Load file from TPDD
  TK.COM:  Kill file on TPDD
  (soon to come:  TCD.COM:  TPDD change directory)


Transfer these programs using IMP80 (and change .COM to .CO for transfer) into CP/M.

How do I get M100 CP/M loaded up?

The best way to get M100 CP/M running with NSC800 is to start with a known good M100 CP/M installation, and then convert the hardware.

The currently posted version of M100 CP/M happens to use 8085 undocumented opcodes. A modified version of M100 CP/M has been prepared that is pure 8080.

CPM440_patched.ZIP 


  This version of M100 CP/M includes the following changes
  1. all 8085 undoc opcodes have been removed, and the code reworked.
  2. a patch has been applied to support the NSC800 version of the BCR hack.

Because stock IMPORT/EXPORT don't work with the NSC800, that problem needs to be solved BEFORE you install the NSC800 CPU.

I modified Philip's IMPORT and EXPORT routines to eliminate the 80C85 undoc opcodes and SIM/RIM. The result are 8080 based versions called IMP80 and EXP80, below.

8080_import_export.zip


Steps to get M100 CP/M and NSC800 running: 

  0.  Modify the M100 to put a socket in place where the 80C85 is.  Install the 80C85 for now.
  1.  Start with a freshly installed REXCPM in an M100, with no CP/M installed.   So, a blank REXCPM.
  2.  Follow Philip's procedures to get an initial M100 CP/M system up and running.  Use the posted files.
  3.  Run M100 CP/M from the laptop LCD, not RS-232 or CASS (BCR).
  4.  Using IMPORT, transfer into CP/M the modified IMP80 and EXP80.  Test that they work as expected.
  5.  Update M100 CP/M to use CPM440_patched.bs, by using CPMUPD.CO.  Change the filename to CPM440.bs.
      Switch back to M100 mode.  Run the command CPMUPD.CO CPM440.bs
      This will update the CP/M operating system.


OK, now you have a system ready to transplant the NSC800. Next.. 

  6.  Open the M100, and install (1) the NSC800 and (2) the modified main ROM.
  7.  Close up the laptop, and power up.  You should see that the NSC800 is working.
  8.  Now, start CP/M and you should be up and running.


Since the NSC800 and RXCMGR are incompatible, use CPM.CO to start CP/M.

For added convenience, I have made a version of CPM.CO as a .DO file, for easy file transfer to the laptop. Use this if your CPM.CO file gets corrupted.

CPM_DO.ZIP

Comments welcome on this procedure!

What about using the BCR Hack for external video?

Ah, great question! As you know M100 CP/M supports 3 types of video 

  1.  M100 native LCD
  2.  VT100 video over RS-232
  3.  VT100 video over (a suitably modified) BCR port

With NSC800 processor, since we don't have the SID or SOD pins nor the RIM/SIM opcodes, the BCR hack needed to change. That change is documented here:

https://bitchin100.com/wiki/index.php?title=BCR_TTL_SERIAL_HACK#NSC800_BCR_Hack

The original hack "V1" uses the SOD pin... not good for NSC800. A more generic hack "V2" uses the Motor on/off relay control to bit bang the Tx serial data at high speed. V2 works for both 80C85 and NSC800.

This change requires a bit of software change to work, though. To make M100 CP/M send video data over this modified BCR hack, a patch is needed.

The patched CPM440.bs file posted above includes this patch.

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