6 - 52
No. 99MBC071A
6.2.4.4 Functions
The GP-IB interface functions include the following.
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TIP What is “serial poll” ?
• The controller which receives an SRQ (Service Request) will call the talkers that it
assumes are transmission sources. When the addressed talker transmits a status
byte (8-bit data) back to the controller to represent the talker condition, the control-
ler will check each byte to identify the source talker.
When the controller calls a talker for this purpose, it sends an SPE (Serial Poll
Enable) to the talker to discriminate from general addressing to the talker.
When this command is issued, the addressed talker will output a status byte to
represent the talker condition. The talker, if it has issued the SRQ, indicates this
by setting the 7th bit of the status byte to “L”.
Therefore, the controller must be programmed so that it jumps to a subroutine to
do with the talker’s request when it identifies the source talker.
When the serial poll mode is completed, the controller will send an SPD (Serial
Poll Disable) for the bus line, and will then return to the normal operation mode.
• SRQ status byte
In the serial poll state the GP-IB interface unit indicates the reason for issuing an
SRQ with the following bit contents:
bit0
(LSB)
bit6 bit1bit5 bit3 bit2bit4
00RSV 00000
0 RSV
Error No.010
01RSV GO00NG1
OK
ERROR
DATA
bit contents
Item
• RSV becomes “1” when this interface is in the service request state.
bit7
(MSB)
bit0
(LSB)
bit6 bit1bit5 bit3 bit2bit4
00RSV 00000
0 RSV
Error No.010
01RSV GO00NG1
OK
ERROR
DATA
bit contents
Item