Measurement Computing Digital488 - Manual (Page 46)

Section 3 Command Descriptions
3.16
F4 Format - Binary
In the F4 binary format, no error checking is performed and caution must be
exercised when using this mode to avoid locking the IEEE bus.
When addressed to listen, the Digital488 expects the "D" prefix followed by five
bytes of data beginning with PORT5 without the "Z" suffix. If any digital I/O port is
configured as an input, the data to that input port will be ignored.
When the Digital488 is addressed to talk (R0) it asserts Inhibit, reads the data
from all ports, unasserts Inhibit and outputs 5 bytes beginning with PORT5 with EOI
asserted on the last bye. Bus terminators, with the exception of EOI, are not appended to
the output. After output the Digital488 must be re-addressed to talk to perform
subsequent reads. EDR (R1) may also be used to capture data in this format.
F5 Format - High Speed Binary
In the F5 high speed binary format, the command interpreter is disabled. When
addressed to listen, the Digital488 treats all bytes received as data to be output to the
Digital I/O ports. Each time it receives five bytes or detects EOI asserted, it pulses the
Data Strobe for approximately 15 microseconds. Data is expected in a PORT5, PORT4,
PORT3, PORT2, PORT1 sequence. If only two bytes are received, with EOI asserted on
the second byte, the Digital488 will update PORT5 with the first byte received, PORT4
with the second and pulse the Data Strobe. Since the interface treats all received
characters as data, the Un command will not be recognized.
To place the Digital488 in the F5 format, the 3 character string "F5X" should be
the last command sent to the interface without terminators. Any characters appended to
this command, such as carriage return or line feed, will be considered data and the output
ports will reflect those character values.
When addressed to talk in this format it asserts Inhibit, reads the data from all
ports, unasserts Inhibit and outputs the binary data to the bus with EOI asserted on the
fifth byte. When the last data byte is transferred, the data is read again in anticipation of
another data transfer. If Inhibit is used to sequence external hardware, this line will pulse
N+1 times; where N is the number of total (5 byte) data transfers. In this format the
Digital488 does not have to be re-addressed to talk to read the ports multiple times. EDR
cannot be used to capture data in the F5 high speed binary format.