Fluke 8842a User Manual download pdf (Page 70)

Remote Programming

INTERFACE MESSAGES

3-29

The SRQ mask can enable any combination of serial poll register bits 1 through 6. Its six-

bit binary representation is ANDed bit-for-bit with serial poll register bits 1 through 6

whenever the output buffer is loaded. If any mask-enabled bit in the serial poll register

comes true, the RQS bit (bit 7) is set true, generating a service request.

Example Explanation

"* N4 P1 ?" An SRQ is generated if the front panel SRQ button is pressed. The string

sets the SRQ mask to 04, which is 000100 in binary. This mask is ANDed

with the lower six bits of the serial poll register. The mask thus enables bit

3, the Front Panel SRQ bit.

The SRQ mask codes can be added to select combinations of conditions.

Example Explanation

"* N5 P1 ?" An SRQ is generated if the SRQ button is pressed or if the trigger results

in an overrange reading. The SRQ mask is set to 05, which is 000101 in

binary.

At power-up or on any device-clear command, the SRQ mask is set to 00 (decimal). This

prevents service requests by holding the RQS bit false under all conditions. For other

examples of the SRQ mask, see the description of the P1 command.

3-52. INTERFACE MESSAGES

The interface messages understood by the 8842A can be separated into the three main

classes described in the IEEE-488 Standard: address messages (AD), universal

commands (UC), and addressed commands (AC). All interface messages described here

originate at the controller.

3-53. Address Messages

Address messages are used by the controller to communicate talk and listen control to

other devices on the bus. Address messages are sent over the eight data lines of the bus

while the controller holds ATN true. Address messages are processed immediately and

are not placed in the input buffer. The address messages are:

• MLA My Listen Address -- Addresses a device to listen

• MTA My Talk Address -- Addresses a device to talk

• UNL Unlisten -- Addresses all listeners to unlisten

• UNT Untalk -- Addresses all talkers to untalk

3-54. Universal Commands

Universal commands are accepted and interpreted by all devices on the bus. The

commands are of two types, multiline messages and uniline messages. Multiline

messages are sent over the eight parallel data lines in the IEEE-488 bus. Uniline

messages are sent over one of the individual interface management lines in the IEEE-488

bus. All universal commands except DCL are processed immediately by the 8842A,

ahead of any device-dependent commands. Only DCL enters the 8842A input buffer.

The 8842A responds to the following universal messages:

ATN Attention -- A uniline message which causes the 8842A to interpret multiline

messages as interface messages (AD, AC, or UC). When false, multiline

messages are interpreted as device-dependent messages.

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Fluke 8842a User Manual Page 70

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