Id Data Circuits; Multiplexer Relay Control - Keithley 7021 Instruction Manual

ID data circuits

Upon power-up, card identification information from each
card is read by the mainframe. This ID data includes such in-
formation as card ID, hardware settling time, and relay and
channel configuration information.
ID data is contained within an on-card EEPROM (U110). In
order to read this information, the sequence described below
is performed on power-up.
1. The IDDATA line (pin 5 of U110) is set from high to low
while the IDCLK line (pin 6 of U110) is held high. This
action initiates a start command to the ROM to transmit
data serially to the mainframe (Figure 6-10).
2. The mainframe sends the ROM address location to be
read over the IDDATA line. The ROM then transmits an
acknowledge signal back to the mainframe, and it then
transmits data at that location back to the mainframe
(Figure 6-11).
3. The mainframe then transmits an acknowledge signal,
indicating that it requires more data. The ROM will then
sequentially transmit data after each acknowledge sig-
nal it receives.
IDCLK
IDDATA
Figure 6-10
Start and stop sequences
IDCLK
IDDATA
(Data output
from mainframe
or ROM)
IDDATA
(Data output
from mainframe
or ROM)
Figure 6-11
Transmit and acknowledge sequence
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Start Bit
1
Start
4. Once all data is received, the mainframe sends a stop
command, which is a low-to-high transition of the ID-
DATA line with the IDCLK line held high (Figure 6-10).

Multiplexer relay control

Card relays are controlled by serial data transmitted via the
relay DATA line. A total of five bytes for each card are shift-
ed in serial fashion into latches located in the card relay driv-
er ICs. The serial data is clocked in by the CLK line. As data
overflows one register, it is fed out the Q's line of the register
down the chain.
Once all five bytes have shifted into the card, the STROBE
line is set high to latch the relay information into the Q out-
puts of the relay drivers, and the appropriate relays are ener-
gized (assuming the driver outputs are enabled, as discussed
below). Note that a relay driver output goes low to energize
the corresponding relay.
Stop Bit
8 9
Acknowledge
Service Information
6-15