Printronix T3204 Maintenance Manual page 91

Connection to the i960 is on the lower byte (bits 0 through 7) of the data bus.
Timing for the device is provided by an 8 MHz clock (U45–12) generated by
U54. An active high reset is connected to pin 24 and an interrupt signal
(U45–18) is inverted by U52 and connected to the 80960JA's internal
interrupt controller. Several events are enabled by the program. One event
that can create an interrupt is the received character when assembled and
waiting to be read by the processor.
FIFO and SRAM
Print and strobe data are written to the FIFO by the 80960JA. The FPGA,
U50, takes the data and with the SRAM performs print dot control.
Ribbon Sensor (T3X04–21 Only)
The sensor circuitry consists of resistors R177 and R178 and connector J11.
Resistor R178 supplies current to the ribbon sensor emitter LED and resistor R177
provides a load for the ribbon sensor photo transistor (emitter follower mode).
When the ribbon mechanism in the printer is operating properly, pulses are
present on U37–2 whenever the transport motor is turning. If pulses are not
present when the transport motor is turning then it indicates that the thermal
transfer ribbon is broken or jammed.
NOTE: If the printer is in direct thermal mode, then software does not
Operator Panel Controls
The Operator Panel contains three key switches, three LEDs, an LCD and six
membrane-type switches. The i960 constantly polls the switch inputs to
determine their status. Resistor networks RN1 and RN2 are used to provide
pull-up resistors for these lines
The indicator LEDs for RIBBON/MEDIA and PAUSE are controlled by the
i960 by latch outputs U2–16 and U2–12 respectively. When the signals are
high the LED is ON and when the chip output is low the LED is OFF.
U23 is an octal transceiver that operates only in the transmit mode. It buffers
the data going to the LCD. Resistor network RN2 prevents the data lines
from floating when the data transceiver is disabled. Resistors R20 through
R27 and capacitors C37 through C44 are used to slow the edge rate of the
data transceiver in order to control EMI (electromagnetic emissions). U22 is
an octal buffer for the membrane switch inputs where resistor network RN1
provides resistor pull-ups for the switches. Capacitors C12 through C18 and
C36 are used for filtering and EMI control.
Circuit Description
monitor the ribbon sensor since the direct mode does not use a
thermal transfer ribbon.
8–7