User's Manual

PMAC User Manual
28 Talking to PMAC
Note:
If using the Option 2 dual-ported RAM, command PMAC by writing values to
specific registers in the DPRAM. PMAC can provide information by placing
binary values in these registers, but the ASCII commands must have been sent
already to PMAC that cause it to take the proper action when these values are
received, and to place the values in these registers.
Control Characters
Other control characters cause PMAC to take an action independent of the alphanumeric characters sent
before it. These control characters can be sent in the middle of a line of alphanumeric command
characters without disturbing the flow of the command. PMAC will respond first to the control-character
command, storing the text string until the <CR> character is received.
Command Acknowledgement
The exact nature of the PMAC acknowledgement of commands and its data response is controlled by I-
variables I3, I4, and I9, with I3 as the most important. If I3 is 1, PMAC acknowledges a valid
alphanumeric command by sending the line-feed (<LF>; ASCII value 10) character back to the host. If
I3 is 2 or 3, it uses the <ACK> character (ASCII value 6) instead. If I3 is 0, it does not provide any
acknowledging character. Regardless of the setting of I3, PMAC responds to an invalid command by
returning the <BELL> character (ASCII value 7).
When working interactively with PMAC in terminal mode, it is often nice to use the <LF> as
acknowledgement because it spaces commands and responses automatically on the terminal screen.
Data Response
When the command received requires a data response, PMAC will precede each line of the data response
with a line feed character if I3 is set to 1 or 3. It will not do so if I3 is set to 0 or 2. PMAC will terminate
each line of the data response with a carriage return character regardless of the setting of I3. For these
commands, the command acknowledgement character — <LF> or <ACK> — is sent after the data
response, serving as an end-of-transmission character. For computer parsing of the response, the <ACK>
should serve as a unique EOT character.
Data Integrity
Variable I4 determines some of the data integrity checks PMAC performs on the communications, the
most important of which is a line-by-line checksum. The Writing a Host Communications Program
section covers this feature in detail.
Data Response Format
Variable I9 controls some aspects of how PMAC sends data to the host. Its setting determines whether
PMAC lists program lines back to the host in long or short form, whether it reports I-variable values and
M-variable definitions as full command statements or not, and whether address I-variable values are
reported in decimal or hexadecimal form.