Fluke Portable Multimedia Player 8842a User Manual
Remote Programming
SERVICE REQUESTS
3
3-27
1.
Status data (from G0, G1, G3, G4, G5, G6, G7 and G8)
2.
Error messages (if an error exists)
3.
Numeric data (from G2 or a trigger)
This means that an error message always overrides numeric data, but status data is sent
even in the presence of an error. However, the status data does not clear the error
message; the error message is sent the next time numeric data is requested.
even in the presence of an error. However, the status data does not clear the error
message; the error message is sent the next time numeric data is requested.
3-49. SERVICE REQUESTS
Service requests let bus instruments get the attention of the system controller. The
requests are sent over the SRQ line (one of the IEEE-488 bus lines). If more than one
instrument on the bus is capable of sending service requests, the controller can learn
which one made the request by taking a serial poll. Each device (including the 8842A)
responds to the poll by sending the contents of its serial poll register. The serial poll
register indicates whether or not the device requested service, and if so, the reason for the
request.
requests are sent over the SRQ line (one of the IEEE-488 bus lines). If more than one
instrument on the bus is capable of sending service requests, the controller can learn
which one made the request by taking a serial poll. Each device (including the 8842A)
responds to the poll by sending the contents of its serial poll register. The serial poll
register indicates whether or not the device requested service, and if so, the reason for the
request.
The 8842A may be programmed to make a service request on user-specified conditions.
The conditions are specified by entering a value for the service request mask (SRQ mask)
with the P1 command. The SRQ mask works by monitoring the serial poll register, which
in turn monitors various conditions in the 8842A.
The conditions are specified by entering a value for the service request mask (SRQ mask)
with the P1 command. The SRQ mask works by monitoring the serial poll register, which
in turn monitors various conditions in the 8842A.
3-50. The Serial Poll Register
The serial poll register is a binary-encoded register which contains eight bits, as
illustrated in Figure 3-9. The controller can read the 8842A serial poll register at any time
by taking a serial poll. Because serial poll register data is loaded directly onto the bus
(instead of being loaded into the output buffer first), reading the serial poll register leaves
data in the output buffer intact.
illustrated in Figure 3-9. The controller can read the 8842A serial poll register at any time
by taking a serial poll. Because serial poll register data is loaded directly onto the bus
(instead of being loaded into the output buffer first), reading the serial poll register leaves
data in the output buffer intact.
Service requests may also be initiated using the front panel SRQ button if it has been
enabled by the SRQ mask.
enabled by the SRQ mask.
The eight bits of the serial poll register are described in Figure 3-9. Note that the SRQ
mask uses bits 1 through 6 to set bit 7 (the RQS bit). When the RQS bit is set true, the
8842A sets the SRQ line true, which generates a service request. A bit is considered true
when it is set to 1.
mask uses bits 1 through 6 to set bit 7 (the RQS bit). When the RQS bit is set true, the
8842A sets the SRQ line true, which generates a service request. A bit is considered true
when it is set to 1.