Model 100 Serial Interface: Difference between revisions
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CPU selection of baud rate is accomplished by loading a divisor into the PIO register through output ports <code>$BC</code> or <code>$B4</code> and <code>$BD</code> or <code>$B5</code>. | CPU selection of baud rate is accomplished by loading a divisor into the PIO register through output ports <code>$BC</code> or <code>$B4</code> and <code>$BD</code> or <code>$B5</code>. | ||
The baud rate selection must be committed by writing <code>$C3</code> to register <code>$B8</code> | |||
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| 38400 || 4 || 64 || 4 | | 38400 || 4 || 64 || 4 | ||
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Here is a practical example of using 38400bps using only BASIC code. This program dumps all RAM contents to the serial port. | |||
1DEFINTA-Z:OPEN"COM:98N1D"FOROUTPUTAS1:D$="":A=FRE("0"):L=VARPTR(D$)+1:M=L+1:POKEL-1,128:OUT180,4:OUT181,64:OUT184,195:FORI=0TO255:POKEM,128+I/2:POKEL,(IMOD2)*128:PRINT#1,D$;:NEXT | |||
== Data Transmission == | == Data Transmission == | ||
Revision as of 15:08, 2 February 2009
Overview
The BASIC ROM provides access to the serial port. BASIC ROM support is well documented elsewhere. This article covers direct use of the IM6402 UART on the Model 100 and Tandy 102.
Configuration
Before the serial port can be used, it must be configured both for serial word format (data bits, stop bits, and parity) and baud rate.
Select RS232 Port
At any given time, either the internal modem or the external RS232 connector may be connected to the UART. This is controllable through software.
For RS232 access, port $B8, bit #3 must be set to 0.
For Modem access, port $B8, bit #3 must be set to 1.
Note that $B8 is shared with other functions, including power control.
Serial Word Format
Port $D8 controls the serial word format.
Actually, any of $D0 → $DF can be used.
| Bit | Function | Settings |
| 0 | Stop Bit Select | 0 → 1 stop bit 1 → 2 or 1.5 stop bits (1.5 if character length is 5, 2 otherwise) |
| 1 | Even Parity Enable | 0 → Odd parity 1 → Even |
| 2 | Parity Inhibit | 0 → Parity 1 → No parity |
| 4-3 | Character Length Select | Bits: 00 → 5 01 → 6 10 → 7 11 → 8 |
| 7-5 | Unused |
Baud Rate
CPU selection of baud rate is accomplished by loading a divisor into the PIO register through output ports $BC or $B4 and $BD or $B5.
The baud rate selection must be committed by writing $C3 to register $B8
| Baud Rate | PIO Divisor |
Port $BD |
Port $BC
|
| 75 | 2048 | 72 | 0 |
| 110 | 1396 | 69 | 116 |
| 300 | 512 | 66 | 0 |
| 600 | 256 | 65 | 0 |
| 1200 | 128 | 64 | 128 |
| 2400 | 64 | 64 | 64 |
| 4800 | 32 | 64 | 32 |
| 9600 | 16 | 64 | 16 |
| 19200 | 8 | 64 | 8 |
| 38400 | 4 | 64 | 4 |
Here is a practical example of using 38400bps using only BASIC code. This program dumps all RAM contents to the serial port.
1DEFINTA-Z:OPEN"COM:98N1D"FOROUTPUTAS1:D$="":A=FRE("0"):L=VARPTR(D$)+1:M=L+1:POKEL-1,128:OUT180,4:OUT181,64:OUT184,195:FORI=0TO255:POKEM,128+I/2:POKEL,(IMOD2)*128:PRINT#1,D$;:NEXT
Data Transmission
Data Reception
I/O Map
| Name | Direction | Port |
| TX | Output | $C8 |
| RX | Input | $C8 |
| RTS | Output | $BA, bit 7 |
| CTS | Input | $BB, bit 4 |
| DSR | Input | $BB, bit 5 |
| DTR | Output | $BA, bit 6 |
Direction indicates both data flow, and whether to use an IN or OUT instruction to read/write to the given pin.
