ZERO-PAGE MEMORY LOCATIONS AND USAGE FOR RS-232 SYSTEM INTERFACE

• $00A7-INBIT - Receiver input bit temp storage.
• $00A8-BITCI - Receiver bit count in.
• $00A9-RINONE - Receiver flag Start bit check.
• $00AA-RIDATA - Receiver byte buffer/assembly location.
• $00AB-RIPRTY - Receiver parity bit storage.
• $00B4-BITTS - Transmitter bit count out.
• $00B5-NXTBIT - Transmitter next bit to be sent.
• $00B6-RODATA - Transmitter byte buffer/disassembly location.

All the above zero-page locations are used locally and are only given as a guide to understand the associated routines. These cannot be used directly by the BASIC or KERNAL level programmer to do RS-232 type things. The system RS-232 routines must be used.

NONZERO-PAGE MEMORY LOCATIONS AND USAGE FOR RS-232 SYSTEM INTERFACE

General RS-232 storage:

• $0293-M51CTR - Pseudo 6551 control register (see Figure 6-1).
• $0294-M51COR - Pseudo 6551 command register (see Figure 6-2) .
• $0295-M51AJB - Two bytes following the control and command registers in the file name field. These locations contain the baud rate for the start of the bit test during the interface activity, which, in turn, is used to calculate baud rate.
• $0297-RSSTAT - The RS-232 status register (see Figure 6-3).
• $0298-BITNUM - The number of bits to be sent/received.
• $0299-BAUDOF - Two bytes that are equal to the time of one bit cell. (Based on system clock/baud rate.)