Digital488 User’s Manual 11-19-01 Getting Started, 2-7
Service (Digital488: Pin 45
Digital488/32/OEM: Pin35)
The Service input is an edge sensitive input capable of generating a bus Service Request (SRQ).
It is enabled with the SRQ command (M1) and defaults to rising-edge sensitive. The Invert command
(I64 ) can be used to program it to be falling-edge sensitive.
IEEE 488 Bus Implementation
The Digital488 implements many of the capabilities defined by the IEEE 488 1978 specification.
These are discussed in the following sections. Those bus uniline and multiline commands that the
Digital488 does not support or respond to include:
Remote Enable (REN) Parallel Poll (PP)
Go to Local (GTL) Parallel Poll Configure (PPC)
Local Lockout (LLO) Parallel Poll Unconfigure (PPU)
Take Control (TCT) Parallel Poll Disable (PPD)
My Talk Address (MTA)
When the Digital488 is addressed to talk (R0) it asserts Inhibit, reads the data from all ports, un-asserts
Inhibit and outputs the data to the bus in the format as defined by the Fn, Pn and Gn commands.
The output bus terminators are appended to the output with the exception of the F4 and F5 formats.
F4 does not append terminators. The output format of F5 will be described separately. After output in the
F0 through F4 formats, the Digital488 must be re-addressed to talk to perform subsequent reads.
In the R1 mode, it will wait for the selected EDR transition before reading the data and formatting it for
output. If the EDR line has transitioned prior to being addressed to talk, the data read at the time of EDR
will be buffered for output when next addressed to talk. If EDR transitions again before the previous EDR
buffered data has been output, the Digital488 will generate an EDR Overrun error and ignore the EDR
read request. After output in the F0 through F4 formats, the Digital488
must be re-addressed to talk
to perform subsequent buffered output of EDR captured data.
In either Rn mode, the Digital488 can send requested status (Un) without affecting the data ports
or Inhibit. After the requested status is output, the presently programmed Rn mode returns.
EDR
cannot be used to capture data in the high-speed binary format (F5). When addressed to talk in this
format it asserts Inhibit, reads the data from all ports, un-asserts 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.
With all Fn formats, using the Digital488 the data is output in a PORT5, PORT4, PORT3, PORT2, PORT1
sequence. Using the Digital488/32/OEM the data is output in a PORT4, PORT3, PORT2, PORT1
sequence.
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