Fluke Biomedical 956A-201-M2 - Manual (Page 59)

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Relay Control Register (Write Only)
The Relay Control Register (U44) is an 8-bit register with clear, and responds to address 400C. Upon
initial power-up (/RESET), the system reset signal sets all outputs low. Data written into U44 remains at
the outputs until a reset occurs or new data is written by /RELAY CONTROL. Table 3-13 lists relay control
write functions.
Table 3-13. Relay Control Register Write Functions
Data Bit Function
D0 Fail Relay and Indicator
D1 Check Source Relay
D2 Warn Relay
D3 Alarm Relay
D4 Aux Relay (optional)
D5 Remote Indicator (not used)
With the exception of the fail bit (DO), all outputs are applied to U48, which is an inverting open collector
driver. The outputs of U48 drive (via the J2 connector) up to five (5) electromechanical relays located on
the relay circuit board, P/N 942-100-70. The relays are used to indicate a High, Warn, Fail, or Auxiliary
(Optional) alarm and to operate a remote check source.
Watch-dog Timer
The fail bit is used as an input to U47-3, a retriggerable monostable multivibrator, which, when set high-
low-high once per second, causes output U47-6 to remain low. Should this high-low-high watchdog timer
sequence fail to occur (under MPU control), U47 will time out and set U47-6 high, causing the fail indicator
on the panel and the fail relay to de-activate. U48 also drives the remote indicator (when used) on the
front panel.
Bargraph (Write Only)
The bargraph addresses are decoded by U5, which is a 1 of 8 decoder. Control line inputs to U5 are
/R/W, /Write02, and /BARGRAPH. When the bargraph address is selected (4020-4025), U5 further
decodes the addresses listed in Table 3-14.
Table 3-14. Bargraph Write Address
ADDRESS STATE
A3 A2 A1
HEX ADDRESS Function LED Driver
0 0 0 4020 Green 1-10 U55, U56
0 0 1 4021 Green 11-20 U57, U58
0 1 0 4022 Green 21-24 U59
0 1 1 4023 Red 1-10 U50, U51
1 0 0 4024 Red 11-20 U52, U53
1 0 1 4025 Red 21-24 U54