8-7
8.2.3 Reading and Clearing the STB register
STB register contents can be read using serial polling or an ∗STB? common in-
quiry. IEEE 488.1 defined STB messages can be read by either method, but the
value transferred to bit 6 (position) varies depending on the method.
STB register contents can be cleared using a ∗CLS command.
(1) Reading the STB register using serial polling (only when a GPIB
interface bus is used)
When IEEE 488.1 defined serial polling is carried out, the device must re-
turn a 7-bit status byte and IEEE 488.1 defined RQS message bit. Accord-
ing to IEEE 488.1, the RQS message indicates whether the device has is-
sued SRQs in the true state. The status byte value is not affected by serial
polling. Immediately after being polled, the device must set the rsv message
in the false state. If the device is polled again before a cause of issuing a
new service request occurs, the RQS message has already been set in the
false state.
(2) Reading the STB register using an ∗STB? common query
The ∗STB? common query causes the device to output STB register con-
tents and one <NR1 NUMERIC RESPONSE DATA> from the MSS (mas-
ter summary status) summary message. The response is the total of the
status register value assigned binary weights and MSS summary message
value. STB register bits 0 to 5 and 7 are assigned weighs 1, 2, 4, 8, 16, 32,
and 128 respectively, and the MSS is assigned weights 64. The response to
the ∗STB? is the same as that to serial polling with the exception that an
MSS summary message appears in bit 6 instead of an RQS message.
8.2 Status Byte (STB) Register
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