Fluke 8842a instruction manual Interface Messages, Address Messages, Universal Commands

Remote Programming 3

INTERFACE MESSAGES

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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