Fluke 5725A instruction manual Eerom, Data Latch, Strobe Lines, Led Driver, Optoisolator Link

5725A

Instruction Manual

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.

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