Measurement Computing Parallel488 - Manual (Page 25)

Section 4 IEEE to Parallel Operation
4.1
IEEE to Parallel Operation
4.1 IEEE to Parallel Mode Operation
This mode of operation is useful in interfacing a parallel device, such as a
Centronics printer, to an IEEE controller or Talk Only device. Data which is sent by the
IEEE controller to the Parallel488 is buffered and transmitted out its parallel port. The
Parallel488 can buffer approximately 24,000 bytes of data from the IEEE input.
The Parallel488 will refuse to accept more data from the IEEE controller when its
buffer memory is full. It does this by preventing completion of the bus handshaking
sequences.
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 IEEE device
does not automatically send a line feed and the receiving parallel 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.
When power is applied to the Parallel488, it will pulse the INIT line on the
parallel interface for approximately 50 microseconds. This is used to reset the parallel
device.
4.2 IEEE Data Transfers
The following methods may be used by the IEEE controller when sending data to
the Parallel488:
4.2.1 Blind Bus Data Transfers
If the IEEE controller does not mind waiting an indefinite time for data
space in the buffer to become available, the data can simply be sent to the
Parallel488. This is referred to as blind data transfers because the IEEE
controller is blind as to whether or not the Parallel488 is capable of
accepting
data. In this case, the bus controller's output data transfer will be held off by the
Parallel488 if it is unable to buffer the data. It will resume accepting IEEE input
data when memory becomes available. This