HP 8340A, Service Manual

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DIRECT 1/0 ADDRESSING
Introduction
Model 8340A - Service
Direct I/0 Addressing is a tool that allows the user to directly access HP 8340A input and output
devices from the front panel. It allows the user to exercise these devices and thus verify their
operation.
Direct I/O Addressing may only be used when the HP 8340A self test passes (CHECK LED I and
II off, see Controller functional group for more information) and the front panel (or HP-IB) is
operational. It should be used when the troubleshooting has progressed to the point where the
signal path has been determined and a specific 1/0 device needs to be checked to verify it is or is
not the cause of the failure. The required equipment is:
*
DVM
*
Logic Probe
*
Extender Boards
*
Jumper Wires
1/0 Device Description
Input devices are used to place data on the data bus for use by the processor. These devices
consist of the HP-IB Interface and input registers/buffers. To test theses devices using Direct I/O
Addressing, a known input must be placed on the device's input and a "read" command
executed to cause· the data to be placed on the data bus and then displayed in the front panel
ENTRY DISPLAY.
Output devices are used to accept data transmitted by the processor on the data bus and then
translate and transmit the data in a form required for use in other parts of the instrument. These
devices consist of DA Cs, 3 to 8 decoders, output registers, and flip-flops. To test these devices
using Direct 1/0 Addressing, a known input must be transmited on the data bus by means of a
"write" command and the output of the device probed by a logic probe or DVM to verify that the
signal was accepted and re-transmitted properly.
Table SA-4 gives a listing of all the input and output devices t.hat can be accessed by Direct I/O
Addressing. The first two columns define the address (Channel/Subchannel) of the 1/0 Strobe
that must be generated to cause the device to be read from or written to. The third column gives
the strobe's mnemonic and the fourth column gives the IC from which the strobe is generated.
The fifth and sixth columns define the IC that is being accessed (destination of the strobe) and
what type of device it is. The final column defines if Direct I/0 Addressing can be used for
troubleshooting the specific device or if a different troubleshooting section should be referenced.
Cross-referencing from an assembly schematic to this table should be done using the I/O Strobe
address shown on the schematic. It will be shown on the schematic as
(x,Ry:)
which corresponds to Channel x, Subchannel y in the table.
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Scans by HB9HCA and HB9FSX