Printronix T3204 Maintenance Manual page 87

Each of the functions listed above are described in detail in the paragraphs
that follow.
80960JA Microprocessor and Microchip PIC16C55 Microcontroller
The 80960JA Microprocessor (U47) is used to format label data prior to
sending the data to the thermal printhead control circuits. The 80960JA
calculates the proper strobe times used for each print cycle, based on
printhead temperature, printhead voltage, etc.
The 80960JA has 32 address lines. The address lines are also used to
transmit and receive data. The 80960JA utilizes a variable bus width
architecture for its data lines. The EPROM memory and DRAM utilize a 32-bit
bus. All other peripherals utilize a 16-bit or 8-bit bus. The 80960JA internal
data bus and storage registers are 32 bits wide.
The 80960JA input clock is derived from the 50 MHz oscillator, U53. This 50
MHz clock signal is divided by 2 by the programmable logic device U54
providing a 25 MHz clock on pin 5 of U54. This signal (CLK1) connects to pin
H14 of the 80960JA. The CLK1 signal sets the fundamental time base for
both the 80960JA core and external bus. Basic timing for the 80960JA bus
operations is 40 ns per bus state.
The 80960JA has an interrupt controller and two counters built-in. The
interrupt controller has eight external interrupts, of which four are used.
These are all active low and their functions are as follows:
The PIC16C55 is an 8-bit microcontroller with its own internal EPROM
program memory. Its program memory is organized 2k x 12. Its external data
bus is 8 bits wide but its internal instruction bus is twelve bits wide. Only 33
instructions exist which are simple and "RISC like".
The PIC16C55 input clock is derived from the 32 MHz oscillator, U55. This 32
MHz clock signal is divided by 2 by the programmable logic device U54
providing a 16 MHz clock on pin 45 of U54. This signal (CLK16) connects to
pin 27 of the PIC16C55. The CLK16 signal sets the time base for both the
PIC16C55 and the Printhead Control FPGA (U50).
The i960 microprocessor and PIC16C55 (PIC) perform a multitude of
functions. The majority of these functions are listed and described in more
detail than previously discussed.
1. The i960 controls the phase lines and enable lines going to the stepping
motor controller circuit.
Circuit Description
interrupt 0 from PIC16C55
interrupt 1 from UART
interrupt 2 from the expansion PCBA connector (optional)
interrupt 3 from 8 Msec clock. This is the main operating system interrupt.
8–3