User's Manual

PMAC User Manual
Talking to PMAC 33
Switch Address Control For PMAC STD
SW1-1 SW1-2 SW1-3 SW1-4 Card Address Default
OFF OFF OFF OFF @0 @0
ON OFF OFF OFF @1
OFF ON OFF OFF @2
ON ON OFF OFF @3
OFF OFF ON OFF @4
ON OFF ON OFF @5
OFF ON ON OFF @6
ON ON ON OFF @7
OFF OFF OFF ON @8
ON OFF OFF ON @9
OFF ON OFF ON @A
ON ON OFF ON @B
OFF OFF ON ON @C
ON OFF ON ON @D
OFF ON ON ON @E
ON ON ON ON @F
Multi-Card Mode Variable
When talking to multiple cards over a single daisy-chained connector, variable I1 should be set to 2 or 3
(usually 2) on every PMAC on the chain for proper communications (usually, I1 is set to 0, sometimes 1,
if it is the only card on the connecting cable). If this setting has not been made already, as would be the
case on the initial connection, simply set I1 to 2 as the first command to the cards, then immediately
address one of the cards. For example, the command string I1=2@0<CR> could be used to set up all the
cards for daisy chained communications, and then address card 0.
Once this setting has been made (and stored with the SAVE command), it is not necessary to issue this
command, but it will not hurt to do so. Setting I1 to 3 rather than 2 disables the CTS handshaking, so the
host cannot hold off characters from a PMAC; typically this is undesirable.
Addressed-Card Actions
The addressed card at any time can accept alphanumeric commands and respond to them. Only it tries to
control the communications and handshake lines back to the host computer. The cards not addressed at a
given time ignore alphanumeric characters sent over the serial port, and their communications and
handshake outputs are tri-stated so as not to interfere with those of the addressed card. The cards not
addressed still can respond to certain control characters (not those querying a card, below), and, of course,
are listening to see if the addressed card number changes.
Simultaneous Addressing
It is possible to address all cards simultaneously for alphanumeric commands with @@ software
addressing. In this case, all cards will accept alphanumeric characters. Card @0 will provide the
handshake response characters. Query commands are not permitted in addressing. If the host sends such
a command in this mode, card @0 will respond with the <BELL> character.
Handling Data Response
When sending commands that require a data response, it is important to ask for data from only one card
per command line (a command line is terminated by the <CR> character), and to accept the response
before querying another card. Otherwise, more than one card may try to control the lines at once when
responding. For example, the command string @1P@2P<CR> could lead to contention as both cards try
to send position data (neither card starts to process the command until it sees the <CR> character).