Fluke 5725A - Manual (Page 88)

5725A
Instruction Manual
4-18
4-26. EEROM
A 2Kb X 8 EEROM (U512) stores 5725A calibration constants plus the date and
temperature of calibration. If the rear panel CALIBRATION switch is in the NORMAL
position, the EEROM is software write disabled. The 6303Y reads the CALIBRATION
switch via bit 1 of port 5 and enables the EEROM when the switch is in the ENABLE
position. The EEROM is selected when A15 and A14 are low, A13 is high (2000 through
3FFF), and either RD* or WR* is TRUE. Writing is controlled by bit 2 of port 7 and the
RESET* line.
The 5725A does not automatically format its own EEROM. The 5725A informs the
5700A Calibrator if a problem has been encountered at power-up. The 5700A assumes
responsibility for formatting the 5725A EEROM.
4-27. Data Latch
The Data Latch (U510) is enabled via LATCHSEL when three conditions are met:
address bit A15 is 0, A14 is 1 (hex 4000-7FFF), and WR* is 0 (true). Data Latch U510 (a
74HCT373) latches information on the external data bus (D0-D7) and sends this
information to the LED latch (U501), Current Amplifier assembly (A2), and the High
Voltage Sense assembly (A6).
4-28. Strobe Lines
The Current Amplifier (A2) and High Voltage Sense (A6) assemblies tie to the Data
Latch external data bus output with latching relay drivers and/or latches. Information is
strobed into the respective relay drivers/latches by the state of any of the seven strobe
lines. The seven strobe lines (STROBE 1-5,21,22) and a clear line (CLR), all asserted
high, are buffered (U503) outputs on port 6. An additional strobe line called
HVSTROBE, for use by the High Voltage Sense and Power Supply assemblies, is
created from STROBE 2 combined with STROBE 2 ENABLE* and HVSUPPLY*.
Line HVSUPPLY* is generated on the High Voltage Sense assembly. The strobe rate
varies from 50 ms for STROBE 2 to over 100 ms for the other strobe lines. The CLR line
opens all relays except K202.
4-29. Led Driver
Front panel LEDs are driven by U501, a 74HCT373 latch, which is capable of sinking 35
mA of LED operating current. An output LOW turns an LED on. The LED driver is
selected by bit 7 of port 5, LEDSEL.
4-30. Optoisolator Link
An optoisolator circuit links the two-channel guard crossing. This guard crossing circuit
and the related 5725A/5700A interconnection reside on the High Voltage Sense
assembly (A6). Serial communication to and from this guard crossing uses the
RECEIVE and TRANSMIT lines, respectively.
When the 5725A is not being used, all cable inputs into the 5700A are tied to the 5700A
guard to shunt noise currents away.