The Ieee Control Status String - Brainboxes PS-307 User Manual

PSI BOX Reference
being addressed to talk. The input sequence is terminated by the
receipt of the number of bytes specified or by EOS received.
The maximum number of bytes allowed to be requested using
the ENTER command is 65535 bytes.
____________________________

The IEEE Control Status String.

One of the great advantages of the IEEE 488 bus it that up
to 16 devices may be simultaneously present on it, without
confusion as to which one we want to use. Each device has a
unique IEEE address, or device number. Each stream of data that
is transferred on the IEEE bus is preceded by addressing bytes
that inform the bus which device is to transmit data and which
devices are to receive the data. But how do we tell the PSI BOX
which device we want next.
The PSI BOX stores a table of data that it uses to inform
itself of which devices to access and in what manner it should
control the bus. This table of data is called the IEEE control
status string. The IEEE control status string also holds
information on parallel and serial poll responses, time out data,
byte counts of data transferred during the previous i/o and many
other interesting parameters. The first field of the IEEE control
status string holds the current IEEE device number, the second
field is that device's secondary address.
The PSI BOX status string can be accessed in two formats.
The STATUS command causes the PSI BOX to send the
string as a series of ascii numbers separated by comma's, it is
about 128 bytes long.
The SHOW command sends the status string back with
explanations. It has each of the fields labeled with text to help
explain its function. The format is ideal for display on an 80
character screen, about 1500 characters are sent. The SHOW
command is intended for interactive debugging by a person, the
STATUS command returns a string that is easier for a program
to handle. The large size of the SHOW response, especially
Page 76
Mode 7 Overview
Chapter 7