Measurement Computing Digital488/80A - Manual (Page 83)

Serial Poll Status Byte
SUMMARY The Serial Poll Status byte is sent upon receiving the Serial Poll ( SPOLL ) command from the IEEE
488 bus controller.
Bit Location Decimal Value Description
DIO1 1 (LSB) Service input transition.
DIO2 2 EDR (External Data Ready) input transition.
DIO3 4 IEEE 488 bus error.
DIO4 8 Not used; always logic 0.
DIO5 16 Ready for more commands.
DIO6 32 Not used; always logic 0.
DIO7 64 Service Request ( SRQ ) bit.
DIO8 128 (MSB) Not used; always logic 0.
DESCRIPTION
The Serial Poll Status byte is sent upon receiving the Serial Poll (
SPOLL ) command from the controller. Refer to the
Service Request Mask ( M ) command description for details on how the Serial Poll Status byte is affected. To enable
each bit to reflect the true status of the device, the appropriate M command must be executed. The significance of
each bit in the Serial Poll Status byte is shown below:
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DIO1 : When enabled by the M1 command, the DIO1 bit is set by a transition on the Service input line, its active
transition state determined by the Invert ( I ) command I64 . DIO1 is cleared after the controller Serial Polls the
Digital488/80A.
DIO2 : When enabled by the M2 command, the DIO2 bit is set by a transition on the EDR input line, its active
transition state determined by the Invert ( I ) command I32 . DIO2 is cleared after the controller Serial Polls the
Digital488/80A.
DIO3 : The DIO3 bit is set when an invalid command is sent to the Digital488/80A. The M4 command enables a
Service Request ( SRQ ) to occur when an invalid command is received. The bit is cleared after the controller
sends the User Status ( U ) command U0 , and reads the status string from the Digital488/80A.
DIO4 : DIO4 is not used, and is always a logic 0.
DIO5 : The DIO5 bit is set after an entire command string has been received and processed by the
Digital488/80A. The bit is cleared while the Digital488/80A is processing commands which have been received
from the controller. When used with the
M16 command, a Service Request ( SRQ ) is also generated when the
DIO5 bit is set. An Execute ( X ) command must be received before the DIO5 bit can be cleared.
DIO6 : DIO6 is not used, and is always a logic 0.
DIO7 : The DIO7 bit is set when the Digital488/80A generates a Service Request ( SRQ ). This is used by the
controller to determine that the Service Request was indeed generated by the Digital488/80A.
DIO8 : DIO8 is not used, and is always a logic 0.
EXAMPLE
PRINT#1,"CLEAR08" Line 1: Reset the Digital488/80A.
PRINT#1,"OUTPUT08;M4X" Line 2: Select SRQ on IEEE 488 bus error.
PRINT#1,"OUTPUT08;F7X" Line 3: Send an invalid bus command. The ERROR and SRQ LED
indicators should light up.
PRINT#1,"SPOLL08" Line 4: The Serial Poll Status byte returned should be 84 ( 64+16+04 ). The
interpretation of this Serial Poll Status byte is as follows:
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64 - The Digital488/80A was the source of the SRQ.
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16 - The Digital488/80A is ready for more commands.
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04 - There is an IEEE 488 bus error.
When the Digital488/80A is Serial Polled, the SRQ LED indicator turns off.
Digital488/80A User’s Manual 967695 Digital488/80A Commands 77