HP 7470A Interfacing And Programming Manual page 133

A computer must issue special commands to initiate and terminate a
serial poll. During a serial poll, a device must be instructed to talk and
the computer to listen. Therefore, a serial poll cannot be executed when
a plotter is in listen-only mode.
TheParallel Poll
Parallel polling can only be done to plotters with an address 0 through
7. Plotters with address settings from 8 through 30 cannot respond to a
parallel poll. The plotter will respond positively to a parallel poll only if
the conditions specified in the P—maskare satisfied and parallel poll
response is enabled. The P—mask parameter of the input mask instruc­
tion, IM, is used to specify which status byte conditions will result in a
logical 1 response to a parallel poll. The response to a parallel poll is
limited to setting the appropriate data line to a logical 1. The line used
is determined by the plotter's address value as shown in the table below: 7
Plotter Parallel Poll HP-IB Data
Address Bit Position Line Number
0 7 8
4AC.ol\'>>—A
>-P-O'lO3\1
6
5
4
3
Plotter Preset Address
7 0 1
To execute a parallel poll, the controller sets the ATN and E01 lines
to 1. The controller reads the eight data lines, and determines from
these lines which instrument on the bus is requesting service. The com­
puter then sends the parallel poll disable command. Not all computers
have parallel poll capability.
It is important to remember that the 7470 will not send a logical 1
unless the P—mask bit value has been changed from the default value of
O and some condition included in the new P—maskvalue is true. The
plotter does not respond to a parallel poll in listen-only mode.
Positive responses to parallel polls will continue to occur until all bits of
the status byte included in the P—maskvalue have been reset to 0. (See
The Output Status Instruction, OS, Chapter 7.)
HP-IB INTERFACING 9-5