Fluke 8842a instruction manual In-Guard Microcomputer

8842A

Instruction Manual

programmed as inputs to prevent contentions between them and the outputs from other ICs which drive them. Data coming into all μC inputs (except pin 38) is ignored.

NOTE

If the A/D IC (U101) is working properly, its watchdog timer briefly interrupts all of the In-Guard Troubleshooting Mode signals every 1.5 sec for a period of about 0.2 sec. (The signals are then re-established.) If this occurs, the main counter in U101 and its watchdog timer are operating correctly. (See step 6, below.)

When the test is complete, turn off the 8842A and remove the short from TP205.

6-42. In-Guard Microcomputer

While the 8842A is in the In-Guard Troubleshooting Mode, check the following in the order shown:

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Figure 6-9. U202 Pin Diagram

6-46