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| == What is this all about? == | | == What is this all about? == |
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| 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 of the NSC800 Z80 processor that is 80C85 like |
| | * continuing to work in the direction of CP/M |
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| This hacks shown here enable 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.
| | 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. |
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| 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.
| | If you have an interested in doing this conversion please get in touch with me at Twospruces at --the google mail service. |
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| Get in touch with me at Twospruces at --the google mail service.
| | 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. |
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| == Acknowledgements ==
| | 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. |
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| I would like to acknowledge and thank those that have contributed to the project:
| | [[Media:NSC800 conversion1.JPG|NSC800 conversion1.JPG]] |
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| '''Philip Avery''' - for efforts with CP/M and attached Video using the VT100 Adapter
| | [[Media:NSC800 conversion2.JPG|NSC800 conversion2.JPG]] |
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| ==Improved BCR Hack==
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| ===CP/M Status===
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| * currently supported in CPM210/410 as CASS video option
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| ===MVT100 Status=== | | == Acknowledgements == |
| * working on implementing support for this new hack
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| === Supported Models ===
| | I would like to acknowledge and thank those that have contributed to the project: |
| * TRS-80 Model 100
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| * a hardware hack for T102 is likely however not explored at this time
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| * a similar hack should be possible for all ModelT versions.
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| === The Hardware Modification ===
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| | |
| === The Software ===
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| ==Original BCR Hack==
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| | |
| ===CP/M Status===
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| * currently supported in CPM210/410 as CASS video option
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| | |
| ===MVT100 Status===
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| * support has been implemented.
| |
| | |
| === 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 ===
| |
| | |
| '''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. '''
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| 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.
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| This page details the hardware change required to transmit at 57600 baud with minimal changes.
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| It can be demonstrated that, in the M100, both serial Tx and Rx is possible at 57600 over the BCR port.
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| | |
| Tx and Rx at higher speeds is more challenging. Tx speeds of up to 128000 baud have been demonstrated.
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| Transmission at this rate requires disconnection of the cassette port Tx filter at C63.
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| If you remove C63 you get better signal quality for TTL serial, but the cassette port is no longer usable.
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| If, like me, you never use the cassette port they it may not be a big deal.
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| The following image shows the modification to the M100 Cassette/BCR port circuitry.
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| [[Image:ckt2.png||center]]<br/>
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| Here we see a strap added from pin 12 of M34 to pin 3 of the BCR port, defining this pin as Tx data.
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| The following image shows the placement of the strap on the secondary side of the M100 PCB.
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| [[Image:layout2.png||center]]<br/>
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| === The Software ===
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| 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.
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| Additionally, I include some code here as examples.
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| ==== 57600 Baud Routines ====
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| Currently both CP/M and my own VT100 driver user 57600, using the modification posted here.
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| The following code can be compiled, and run in Model 100 to demonstrate transmission between 2 machines at 57600.
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| Tx routine:
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| [[Media:keysnd_57600.zip|keysnd_57600.asm]]
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| Rx routine:
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| [[Media:bcrx_57600.zip|bcrx_57600.asm]]
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| 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.
| |
| | |
| ==== Higher speed Tx Routines ====
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| Faster transmission is possible; both 115600 and 128000 baud have been demonstrated. The core Tx routines are provided here.
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| for Tx at 57600 baud:
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| [[Media:bcrtx_57600.zip|bcrtx_57600.asm]]
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| for Tx at 115600 baud:
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| [[Media:bcrtx_115600.zip|bcrtx_115600.asm]]
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| for Tx at 128000 baud:
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| [[Media:bcrtx_128000.zip|bcrtx_128000.asm]]
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| ==== Timing for 57600 Baud ====
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| 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).
| |
| 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.
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| For CP/M and REXCPM backup/restore this means
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| 4MB backup restore time could be about 12 minutes @57600 baud
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| -- assuming "large packet support" on LaddieAlpha, and direct writes to block RAM.
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| What about 115600 or 128000 baud? While the Tx side has been shown to work, the Rx side is the challenge.
| |
| 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.
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| A quick look at BCRX.ASM above suggests the RX bit reception time could be reduced to 29 clock cycles, supporting ~85000 baud.
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| | '''Philip Avery''' - for efforts with CP/M and attached Video using the VT100 Adapter |
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| [[Category:Model T Hardware]] | | [[Category:Model T Hardware]] |
Work in progress!
What is this all about?
Motivated by 2 things
- discovery 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.
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.
NSC800 conversion1.JPG
NSC800 conversion2.JPG
Acknowledgements
I would like to acknowledge and thank those that have contributed to the project:
Philip Avery - for efforts with CP/M and attached Video using the VT100 Adapter
