TransAct Ithaca 8000, Programmer'S Manual

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Communications Ithaca
®
8000 Programmer’s Guide
100-06908 Rev D Page 275
Some systems may wish to change the details of how the strobe, busy, and
acknowledged signals interact. The parallel-port option features define how the strobe,
busy, and acknowledged signals operate. In normal mode, the printer follows the
standard (Centronics) parallel-port conventions. With Options 1 and 3, the
acknowledged and busy signals change simultaneously, which is sometimes referred to
as ack-after-busy. Options 2 and 3 force busy high on the rising edge of the strobe,
which is sometimes referred to as busy-while-strobe timing. In all cases, the data is
latched on the rising edge of the strobe. In most cases, the normal timing mode gives
the best results.
Figure 17 Parallel Port ACK Timing Options
Legend Time Interval Minimum Maximum
t1 DATA Setup to STB 0.5 uS
t2 STB Width 0.5 uS 500 uS
t3 DATA Hold after STB 0.5 uS
t4 BUSY Delay after STB 0 0.5 uS
t5 ACK Pulse Width 2.5 uS
Table 55 Parallel-port Timing
Note: Altered STB timing to take data on the falling edge of STB can be generated as a
factory option.
Printer Buffer Size
The Ithaca
®
8000 printer has a configurable buffer size. It can be set from 40 to 8192
bytes. The configurable buffer allows an application to control how far ahead the buffer
gets from the printer. The smaller the buffer, the tighter the control will be. It is up to the
application developer to select the optimal buffer size.
Parallel Port Inquire and IEEE 1284
The Ithaca
®
8000 printer supports the IEEE 1284 bidirectional parallel peripheral
interface standard. The IEEE 1284 standard provides for a bidirectional link on the
parallel port. The Ithaca
®
8000 Printer only supports Modes 0 and 4, which provide a
nibble mode reverse channel for printer identification and status inquire commands. It is
Data
STB
BUSY
ACK
ACK
ACK
ACK-while-BUSY
ACK-in-BUSY
ACK-after-BUSY
t1
t2
t3
t4
t5