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PMAC 2 Software Reference

PMAC I-Variable Specification 23

............................ ; PMAC responds with requested data

With I3=3:

#1J+<CR>......... ; Valid command not requiring data response

<ACK>................ ; Acknowledging character

UUU<CR> ........... ; Invalid command

<BELL>.............. ; PMAC reports error

P1..3<CR> ...... ; Valid command requiring data response

............................ ; PMAC responds with requested data

See Also

Talking to PMAC

Writing a Host Communications Program

I-variables I4, I6, I58

I4 Communications Integrity Mode

Range

0 .. 3

Units

none

Default

Remarks

I4 permits PMAC to compute checksums of the communications bytes (characters) sent

either way between the host and PMAC, and also controls how PMAC reacts to serial

character errors (parity and framing), if found. Parity checking is only enabled if jumper

E49 is OFF for PMAC-PC, -Lite, -VME; or ON for PMAC-STD.

The possible settings of I4 are:

Setting Meaning

0 Checksum disabled, serial errors reported immediately

1 Checksum enabled, serial errors reported immediately

2 Checksum disabled, serial errors reported at end of line

3 Checksum enabled, serial errors reported at end of line

Communications Checksum: With I4=1 or 3, PMAC computes the checksum for

communications in either direction and sends the checksum to the host. It is up to the host

to do the comparison between PMAC’s checksum and the checksum it computed itself.

PMAC does not do this comparison. The host should never send a checksum byte to

PMAC.

Host-to-PMAC

Checksum: PMAC will compute the checksum of a communications line

sent from the host to PMAC. The checksum does not include any control characters sent

(not even the final Carriage-Return). The checksum is sent to the host immediately

following the acknowledging handshake character (<LF> or <ACK>), if any. Note that

this acknowledging and handshake comes after

any data response to the command (and its

checksum!). If PMAC detects an error in the line through its normal syntax checking, it

will respond with the <BELL> character, but will not follow this with a checksum byte.

Note:

The on-line command <CTRL-N> can be used to verify the

checksum of a command line before the <CR> has been sent. The

use of <CTRL-N> does not affect how I4 causes PMAC to report a

checksum after the <CR> has been sent.