Fluke 5720A service manual Rear Panel Relay Control, Rear Panel CPU Interface

Models: 5720A

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2-213. Rear Panel Relay Control

5700A/5720A Series II Calibrator

Service Manual

Oscillator Output assembly theory of operation for a detailed description on the generation of P SHIFT. Resistor R18 serves as overcurrent protection for the BNC shell connection on J5.

2-213. Rear Panel Relay Control

The relays on the Rear Panel assembly are used as the interfaces for the 5725A amplifier, or for switching the PHASE LOCK IN and VARIABLE PHASE OUT signals.

The relay switching circuitry is under control of the guarded digital bus via connector J8. This guarded digital bus is generated on the Regulator/Guard Crossing assembly (A17).

The relay control circuitry is located on sheet 5 of the Rear Panel schematic. This circuit uses an 82C55 programmable peripheral interface (U14) and two relay drivers (U16 and U17) to control the 12 relays on this assembly and one relay (K12) on the Analog Motherboard. The 82C55 (U14), which is under control of the guarded digital bus via connected J8, has three ports generating 24 outputs.

Port A (PA0-PA7) provides the input lines for relay driver U16.

Port B (PB0-PB7) provides the input lines for relay driver U17.

PC0-PC2 of port C provides the CLEAR, STROBE, and OUTPUTENABLE lines for these relay drivers.

Relay Driver U16 controls two latching relays (K2 and K3) and four non- latching relays (K1, K4, K5, and K7). Relay driver U17 controls one latching relay (K6) and five non latching relays (K8-K12). Relay driver U17 also creates control line RLY12* (pin 13) which controls relay K12 on the Analog Motherboard assembly (A3).

2-214. Rear Panel CPU Interface

The rear panel is interfaced to the CPU assembly (A20) via connector J8 on the rear panel. The CPU has:

Five address lines (RPA1-RPA5) which comprise the ADDRESS BUS

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Page 196
Image 196
Fluke 5720A service manual Rear Panel Relay Control, Rear Panel CPU Interface