Operation
4-9
4.6.4 Stand-alone and master/slave
One method for expanding system size is to connect up to
five switching systems in a master/slave configuration,
where all units are daisy-chained for serial communication
and control. System operations are performed through the
master unit, either over the IEEE-488 bus or the master’s
front panel (including the light pen). A master/slave system
appears as a single unit and IEEE-488 address with a maxi-
mum size of 8 rows by 60 columns. Select stand-alone or
master/slave operation by setting the IEEE-488 addresses of
the Model 708A Switching Systems. Use the rotary switches
located on the rear panel of the Model 708A.
As described in paragraph 3.5.4, the MASTER/SLAVE OUT
and MASTER/SLAVE IN rear panel connectors are used to
connect DIN cables in a closed loop. The connector pinouts
are defined in Figure 4-10. The rear panel IEEE-488 address
switches are shown in Figure 4-11.
Designate one unit to be master by adding 30 to the IEEE-
488 address (selectable by rotary switches on the rear panel
of the Model 708A). If the loop of DIN cables is not closed,
the master’s error LED (ERR) will light, and all units will re-
main as stand-alones.
CAUTION
When it is necessary to cycle power on a
slave unit, turn off all units in the mas-
ter/slave configuration. This procedure
prevents the open communication and
control loop from putting the slave unit
in an undesirable state.
Figure 4-10
Master/slave connectors
Pin Master/Slave IN Master/Slave Out
1 M/S TRIGGER (low true)
M/S TRIGGER (low true)
2 ALLREADY
ALLREADY
3 LPRESET (low true)
LPRESET (low true)
4 LPSENSE (low true)
LPSENSE (low true)
5 RxDATA
TxDATA
6-8 Chassis Ground
Chassis Ground
2
1
8
AAA
AAA
A
A
A
A
4
5
6
7
3
Cycle power of all units in the master/slave loop to establish
control of the slaves through the master. During master/slave
operation, most front and rear panel controls of the slave
units are inactive. Table 4-4 shows slave unit’s control and
indicator status.
The master unit communicates with the slaves only when
necessary; it does not continuously monitor the status of the
closed-loop configuration. Hence, a disconnected master/
slave loop cable will not be detected and the ERR LED will
not be lit until the master attempts to send or receive data
around the loop. To determine if a master/slave error has oc-
curred, send a DDC (refer to paragraph 5.9.20). The steps to
recover from an master/slave error are:
1. The master stops processing IEEE-488 bus commands,
returns to stand-alone operation, and terminates.
2. The slave units remain the same as before the error oc-
curred.
Table 4-4
Slave unit controls, indicators, and connections
Switch, indicator, or connector
Slave unit status
Front Panel
POWER
CROSSPOINT DISPLAY LEDs
LOCAL key
OPEN RELAYS key
TALK, LSTN, REM LEDs
Light Pen/Light Pen Connector
Rear Panel
MASTER/SLAVE IN
MASTER/SLAVE OUT
EXT TRIG INPUT
MATRIX READY OUTPUT
DIGITAL INPUT and OUTPUT
IEEE-488 INTERFACE
active
active (display only)
inactive
inactive
inactive
inactive
active
active
inactive
active
(timing accuracy
may be inaccurate)
inactive
(outputs set to low)
not used
0
1
2 34
5
678
9
IEEE-488
ADDRESS
0
1
2 34
5
678
9
Figure 4-11
Rear panel – IEEE-488 address switches
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