Measurement Computing Parallel488 - Manual (Page 19)

Section 3 Parallel To IEEE Operation
3.1
Parallel To IEEE Operation
3.1 Parallel to IEEE 488 Mode Operation
The Parallel To IEEE mode allows a parallel (Centronics) host device to send
data to single or multiple IEEE bus peripherals. The Parallel488 accepts characters on
its parallel port and outputs them to the IEEE port. The interface can buffer
approximately 24,000 bytes of data from the parallel port. Applications include
interfacing a listen-only or addressable IEEE printer/plotter to a parallel printer port.
The Parallel488 will refuse to accept more data from the parallel port when its
buffer memory is full. It does this by preventing completion of the parallel bus
handshaking sequence.
The Parallel488 also has the capability to automatically insert a line feed
character after receiving a carriage return character. This is necessary if the sending
parallel device does not automatically send a line feed and the receiving IEEE device
does not automatically insert a line feed. It will become immediately evident that this
feature should be enabled if your printed material all appears on one line.
3.2 Parallel Data Transfers
At power on, the Parallel488 sends an Interface Clear command on the IEEE
bus for greater than 100 microseconds. It then sends the following IEEE command
sequence ofÉ
ATN UNL,UNT,LAG,*ATN
In this sequence, LAG includes all listen addresses from 0 to 30. This guarantees that
any printer or plotter attached to the Parallel488's IEEE port will be in the listen mode,
ready to accept characters. A device on the IEEE port which is in the LISTEN ONLY
or LISTEN
ALWAYS mode will also be ready to accept characters. The power-on
sequence is also initiated when the INIT line is detected by the Parallel488 on the
parallel bus.
After all devices have received their listen address, the Parallel488 will accept
characters on its parallel port and output them to the IEEE port. If characters are