Datasheet

Chapter 2 — Theory of Operation
20 PB42 Portable Receipt Printer Service Manual
Error Detection
When the print controller encounters an error condition it asserts the
ERROR* interrupt (IRQ7). The error type is encoded on three signals:
ERR0, ERR1, and ERR2. These are connected, respectively, to bits 2, 1,
and 0 of the input shift register. The error codes are given in the table
below:
Upon receipt of an ERROR* interrupt the error code should be read by the
processor through the input shift register. See section 2.6.2 Input/Output
Shift Registers for details.
Thermistors and Paper Sensors
The print controller monitors the temperature of both the print head and
the ambient air (main PCB). These thermistors are also connected to the
serial ADC. The print head thermistor, SHTH is connected to channel 4
and the ambient thermistor, ENVT, is connected to channel 0.
There are 3 optical paper sensor outputs that can be read by the processor:
• PAPER_SENSOR0
• PAPER_SENSOR1
• PAPER_SENSOR2
The first two are also monitored by the print controller. They are
respectively connected to ADC channels 1, 2, and 3.
The last two (1 and 2) are optional sensors that are connected to Auxiliary
Sensor Connector, J3. These can be used as mark and/or gap sensors. These
sensors are not used in the PB42.
PAPER_SENSOR0 is an out-of-paper sensor. Since this is also monitored
by the print controller, an out of paper condition will generate a print
controller error.
For details on how to read voltages of the thermistors and paper sensors, see
“Analog to Digital Converter” on page 16.
Error Codes
Printer Status !ERROR ERR0 ERR1 ERR2
Initialize Low Low Low Low
Hardware error Low High Low Low
Out-of-paper error Low High High High
Platen position error Lor Low High High
V
p
voltage error Low High Low High
Head temperature error Low Low Low High
Stop mode High High High High
Return-waiting status High High Low High
Print-ready status High Low Low High