DS1410E Datasheet, PDF (3/7 Pages) Dallas Semiconductor – Parallel Port Adapter

DS1410E
PRINTER COEXISTENCE
In order to coexist with parallel port printers, the DS1410E utilizes output pins 11 and 13 and input pins
11 and 13. When input pin 14 is low these pins are used for transmitting data received on the I/O pin or
for issuing an unmistakable busy signal. When input pin 14 is inactive (high) input pins 11 and 13
propagate the states of output pins 11 and 13.
If a printer is attached to a DS1410E, output pin 11 is connected to the printers BUSY signal (low only if
printer is on-line and busy), and output pin 13 is connected to SELECT OUT (driven low if printer is off-
line), see Figure 2.
If the attached printer is “powered up” and on-line, the DS1410E uses SELECT OUT for communication
regardless of the state of the printers BUSY signal. If the printer is offline its BUSY signal is inactive
(high) and this line is used by the DS1410E for host communication.
If the attached printer is powered off, both SELECT OUT and BUSY will be low. This prevents
meaningful communication with the DS1410E because it is unable to de-assert its busy signal (input pins
11 and 13 low) or return a high sample of the I/O pin.
To solve this problem, the DS1481 uses the busy signal issued during a reset to detect the presence of
another DS1481 based device attached behind it on the parallel port. If this busy signal is not detected by
the DS1481, it assumes that it is the last DS1481 based device on the port.
If the DS1410E determines that it is the last device on the port it ignores the states of output pins 11 and
13 while input pin 14 is low. It also leaves the output pin 14 high to prevent sending line feed signals to
the printer. This gives the last device the ability to control input pins 11 and 13 without affecting
stackability.
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