Fluke 8842a instruction manual IEEE-488 Interface Option, Out-Guard Microcomputer, Guard Crossing

8842A

Instruction Manual

5-37. IEEE-488 INTERFACE (OPTION -05)

The IEEE-488 Interface has five major parts, as shown in the block diagram in Figure 5-

16.All components are contained in a single printed circuit assembly (PCA). Reference designations are numbered in the 900 series.

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Figure 5-16. IEEE-488 Interface Block Diagram

5-38. Out-Guard Microcomputer

The Out-Guard Microcomputer (μC) (U901) communicates with the IEEE-488 talker/listener IC (U911) and the In-Guard μC (U202).

The Out-Guard μC is similar to the In-Guard Z8 μC except that is contains 8K bytes of ROM and 236 bytes of RAM. For futher description of the Z8 μC, refer to the heading "In-Guard Microcimputer, " above.

5-39. Guard Crossing

The guard crossing circuit permits serial asynchronous communication between U901 and U202 while isolating the two electrically. One-half of the guard crossing circuit is contained on the Main PCA; the other half is on the IEEE-488 Interface PCA. Operation of the guard crossing circuit is described in an earlier heading.

5-40. Bus Interface Circuitry

The IEEE-488 bus protocol is handled by the uPD7210 IEEE-488 talker/listener IC (U911). It is controlled by U901 as a memory mapped peripheral through an 8-bit data bus.

Bus transceivers U912 and U913 buffer U911 from the IEEE-488 bus. They provide the bus with the required output drive capability and receiver impedance.

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