Embedded Files
I was given some old HP Laserjet 4P printers, liked that they had Vacuum florescent (VFD) Display board, thought it would be cool to see if I could use it with my Z80 SBC project.
I very old school hacking taking things from other devices and re-using them in my own projects. For those who are new to the world of 8-bit and hacking hardware for new uses.
The first thing is to find the main chips and look up their datasheets, this will help us decode how the board was interfaced to the printer.
The VFD display driver chips is the M66004FP simple google search was able to find the datasheet and the device is a clock driven serial data input only with a -40 volt display bias but looked at board notice the round transformer on the board indicates the power supply for that is built on the board so we don't have to worry about that voltage. the keyboard buttons are read by the 74HC165 8 input shift register. So have now have how many data signals we will need, from the datasheet we can come up with the following minimum signals needed: Clock, Enable display, enable keyboard, data in, data out.
Looking at the connector to the board, we have 9 wires coming into the board (image Rear view), on either end of the 9 points where the wires solder in, two of them are soldered together making a good guess that is power in. With a meter I was able to measure from the filter capacitor Positive and Negative terminals which side of the pins where positive and negative. So now we have eliminated 4 pin of the 9 pins and now know their function. Since I could not see a Pin 1 marker for the connector I went with the right side as pin 1.
Connector
1 +5 volts2 +5 volts345678 Ground9 GroundNow we need to find out the remaining 5 connection points, so with a meter and looking at the chips pin-out on the data sheet, I tested the most likely pins to be used to see which ones go to the Connector. Note I notice that each connection goes through a 100 ohm resistor, so when reading knew I would not get zero on my meter but should be 100 ohms.
Going with the M66004FP Datasheet chip outline (Image below) , filled in the next few, then used the 74HC165 Datasheet to find the next
Connector
1 +5 volts2 +5 volts3 Serial data input to display4 Shift clock input shared by both chips5 Chip select Display6 Shift Register Load parallel data7 Shift Register out8 Ground9 GroundHow that we have our pin-out of the connector and know there function, let's look at what we need to get data in and out of the board. Four of the pins are inputs and one output, since I built my board using the Z80 PIO, it allows you to program each port bit as a input or output saving from having to use two ports.
M66004FP chip pinout
M66004FP chip pinout
74HC165 chip pinout
74HC165 chip pinout
Front view
Front view
Rear view
Rear view
The basic's of reading and writing to the board, this program uses the Z80 PIO to interface to the board and my Z80 PIO library
#include "hp_dis_in_brd.h"
int HP_read_buttons( void ){int i, k, j;
// make sure out PIO is set correctj=0;z80_outp( Z80_PIO_A_CTL, Z80_PIO_M3); // set mode 3 Port Bit set per maskz80_outp( Z80_PIO_A_CTL, 0x87); // z80_pio_write_bit(Z80_PIO_A, 6, 1);z80_pio_write_bit(Z80_PIO_A, 4, 1);// Shift bit's out left, LSB-MSB// Write address to read
z80_pio_write_bit(Z80_PIO_A, 6, 0);z80_pio_write_bit(Z80_PIO_A, 6, 1);for(i=0; i < 8; i++) { j = j<<1; j= j | (0x01 & z80_pio_read_bit(Z80_PIO_A, 7)); z80_pio_write_bit(Z80_PIO_A, 4, 0); z80_pio_write_bit(Z80_PIO_A, 4, 1); }k = j; return k;}
void HP_write_str( char *ptr ){HP_display_write(0xf5 ); // auto increase on while ( *ptr != '\0' ){HP_display_write( *ptr++ );}
HP_display_write(0xf4 ); // auto increase off }
void HP_display_write(char cmd ){char i, j;// make sure out PIO is set correctz80_outp( Z80_PIO_A_CTL, Z80_PIO_M3); // set mode 3 Port Bit set per maskz80_outp( Z80_PIO_A_CTL, 0x87); // D0-D2 reserved set inputs, D3-D6 set output, D7 set to input.
j = cmd;z80_pio_write_bit(Z80_PIO_A, 5, 1);z80_pio_write_bit(Z80_PIO_A, 4, 1);z80_pio_write_bit(Z80_PIO_A, 5, 0);// Shift bit's out right, MSB-LSBfor(i=0; i < 8; i++) { z80_pio_write_bit(Z80_PIO_A, 4, 0); z80_pio_write_bit(Z80_PIO_A, 3, j & 0x80 ); z80_pio_write_bit(Z80_PIO_A, 4, 1); j = j<<1; }z80_pio_write_bit(Z80_PIO_A, 5, 1);}
/* hp_dis_in_brd.h *//* HP LaserJet 4P display/input board routine *//* 16 character VFD display chip M66004FP *//* 9 buttons input chip 74HC165 paralell in serial out *//* Pinout of board connector I calling pin 1 nearest 1 one of display chip *//* 1 & 2 VCC *//* 3 Serial Data in */ /* 4 Shift Clock/Display Clock *//* 5 Display CS *//* 6 Shif-register (CP) Load *//* 7 Shift-register out, 8 & 9 ground */
#include "z80_pio.h" #include <z80.h>#include <stdlib.h>#include <stdio.h>
/* Display Controll registerDisplay digit length 0x00 9 digits0x01 10 digits0x02 11 digits0x03 12 digits0x04 13 digits0x05 14 digits0x06 15 digits0x07 16 digitsDisplay Dimmer value setting0x08 1/160x09 2/160x0a 4/160x0b 6/160x0c 8/160x0d 10/160x0e 12/160x0f 14/16One-digit display frequency setting0xf6 128/fosc0xf7 256/foscDisplay digit position 0xf? ?=0-f Display auto increment 0xf4 off0xf5 onDisplay ON/OFF0xf0 display off0xf1 display on0xf3 all segments on. Cursor off0x8? 0-fCursor on0x1? 0-f
*/
void HP_display_write(char cmd );
void HP_write_str( char *ptr );
int HP_read_buttons( void );
Example of sending data to display and reading key's to change display
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