3860/80 User’s Manual
12-8
Buffer Options
At the time the printer is shipped, and again at initialization, the input data buffer size is 4K,
the high trip point is 256 bytes below the top of the buffer, and the low trip point is 256 bytes
above the bottom of the buffer. These buffer parameters can be changed from the Interface
Parameters option on the Printed Menu, and the printed status sheet shows the current buffer
settings. The buffer size can be set from 2K to 63K in 1K increments.
When the buffer fills to the high trip point, the printer sets a BUSY condition at the interface to
tell the host to stop sending data. When the printer empties the buffer down to the low trip
point, it sets a READY condition at the interface to tell the host to send more data.
The band between the high trip point and the top of the buffer applies to the serial interface
only. The parallel interface will not honor a STROBE pulse while BUSY is asserted. Therefore,
when the parallel interface is used, whatever is set as the high trip point will be the top of the
buffer.
The reason for the band between the high trip point and the top of the buffer is to allow receipt
(and thus prevent loss) of data while the host reacts to BUSY. The default works in most
cases, but, on some systems, there is significant delay between the time the printer goes
BUSY and when the data source responds to the message. The reason for the band between
the bottom of the buffer and the low trip point is to give the printer data to process while the
host reacts to the READY signal.
There can be as much as 4K of buffer capacity downstream of the input buffer. This
downstream buffer capacity is not user-adjustable. Therefore, there is always more net buffer
capacity than is indicated by the buffer menu.
DATA IN
DATA IN
BUFFER CYCLE
HIGH TRIP POINT
LOW TRIP POINT
READY BUSY
BUSY
BUSY
READY
