Fluke How the 5700A and 5725A Communicate, 4-10, Description of the Out-GuardLines 5725A Side

5725A

Instruction Manual

How the 5700A and 5725A Communicate 4-10.

The 5725A and 5700A maintain all analog and digital communication over an external cable connected to subminiature D-type connectors on the back of each instrument. All in-guard (analog) signals, except B-VGRD, connect to relays that isolate the 5725A and 5700A whenever the 5725A is not in use.

Digital communication occurs over five out-guard (digital) 5700A lines, B-SCT, B-SCR, B+5V, B+5VCOM, and B-CINT*. The B+5V and B+5VCOM lines power the 5725A guard crossing and allow the 5725A to detect when the cable is disconnected. Lines B- SCT and B-SCR provide serial communication of data over an RS-232 type line. Optoisolators on the 5725A maintain the integrity of the guard. Line B-CINT* is a hardwire loop that allows the 5700A to detect a cable off or 5725A power off condition.

Description of the Out-Guard Lines (5725A Side) 4-11.

The following list describes the five 5725A out-guard lines:

∙B-RCV (Serial Communication Receive)

Receives serial data from the 5700A; connects to the B-SCT line of the 5700A.

∙B-XMIT (Serial Communication Transmit)

Transmits serial data to the 5700A; connects to the B-SCR line of the 5700A.

∙B+5V

5700A out-guard supply that powers optoisolators and 5725A CABLEOFF relay.

∙B+5VCOM

5700A out-guard supply common for above.

∙B-CINT* (Boost Cable Interlock)

Hardwire "loop around system" on the 5725A that is polled at least every 100 ms by the 5700A to determine if the 5700A/5725A cable is connected and if the 5725A is turned on. Returns a low to the 5700A if above is true. A pull-up resistor on the 5700A leaves this line high if the interconnect cable is open or if the 5725A is turned off.

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