Printronix T3204 Maintenance Manual page 97

RS422 Drivers and Receivers
The RS422 driver and receiver are contained in one chip (U39). This chip
contains two RS422 drivers (only 1 is used) and two RS422 receivers. Resistor
R118 is a line terminating resistor used to match the receiver input impedance to
the impedance of the transmission line. The resistors R91 and R119 are used to
force the output of the RS422 receiver HIGH when the RS422 input is not in use
(i.e., not connected). The unused RS422 receiver circuit receives its input from
the low-power reset (Q1). The resistors R134 and R135 are used to bias U39–6
to +2.5 volts. When U39–7 goes above +2.5 volts then U39–5 will go LOW. When
U39–7 goes below +2.5 volts then U39–5 will go HIGH. When U39–2 is more
positive than U39–1 then U39–3 will go HIGH. When U39–2 is more negative
than U39–1 then U39–3 will go LOW.
When U39–5 is HIGH then U39–14 will be HIGH and U39–13 will be LOW.
When U39–15 is LOW then U39–14 will be LOW and U39–13 will be HIGH.
U39–4 is an enable input for the RS422 driver that can be controlled from the
UARTs (U45) RTS output.
Analog-to-Digital Converter
U29 is a single channel analog to digital converter with parallel access. It is
fed by an eight-channel analog multiplexer (U37). In addition to the
start-of-print adjustment available on channel U37–5 as previously
discussed, the remaining channels of U37 are used as listed.
Channel 0
Channel 1
Channel 2
Channel 3
Channel 4
Channel 5
Channel 6
Channel 7
Programmable Jumpers and Switches
The following is a list of the proper settings for jumpers on the Printer
Controller PCBA.
EPROM
DRAM
32 MHz Oscillator
50 MHz Oscillator
Circuit Description
– Printhead thermistor
– Paper edge detector
– Monitor +24 volts
– Reserved
– Spare
– Reserved
– Ribbon sensor
– Spare
2 MB Jumper on E2–E4 and E6–E7 (Factory setting)
1 MB Jumper on E16–E17 (Factory setting)
5 MB Jumper on E20–E21
17 MB Jumper on E22–E23
Enabled Jumper on E45–E46 (Factory setting)
Enabled Jumper on E43–E44 (Factory setting)
8–13