Communication Interfaces; Data Input Buffer; Buffer Size And Ready Ibusy Points - Texas Instruments 880 User Manual

Section 7
Communication Interfaces
This section describes the two methods of com-
munication between the Model 880 and its host
computer. The communication can be through
either a serial or a parallel connection. You select
the appropriate type of printer/host interface by
choosing the configuration code while the printer
is in the menu mode (see Section 3).
7.1 DATA INPUT BUFFER
All data received by the printer is temporarily
stored in a first-in-first-out (FIFO) input buffer.
The operational size of the input buffer is deter-
mined by the physical size of the buffer installed
(2K bytes standard, 4K bytes or 16K bytes
optional) and the setting of configuration code
9C.
To prevent data from being lost when the printer
receives data at a higher speed than the printer
can print, the printer transmits "BUSY" to the
host. The "BUSY" signal stops the host from
sending data. The printer transmits "READY" to
the host when more data can be put into the
buffer. The buffer sizes and READY/BUSY points
are shown in Table 7-1.
Table 7-1.
Buffer Size and READY/BUSY Points
Config. Code 9C - OFF
Code
9C-ON
2Kbytes
4K bytes 16K bytes
Buffer size, serial 256 2048 4096 16384
and parallell/F characters characters characters
characters
BUSY point, 249 1792 3840 16128
seriall/F only characters characters characters characters
BUSY point, 256 2048 4096 16384
parallell/F only characters characters characters characters
READY point, serial 121 1280 2816 15104
and parallell/F
characters
characters characters characters
7-1