Tom's Life Bits

The VeriFone Tranz 330 is one of those ubiquitous credit card readers you see all over the place.

Looks like it's a Z80 based board. Inside, it's all 5V, but it has a voltage regulator so you can plug a 7.5V-9V AC Adapter into it.

Inside, it's two pieces. There's the bottom board (the motherboard), that has all the intelligence, and a top board with all the peripherals on it, like an alphanumeric display, a keypad, a piezo speaker, and the mag stripe reader.

Conveniently, the top board and bottom board are connected through a .1“ spaced header. This makes it easy to hack.

I suppose I could flash some Z80 machine code onto that EPROM? But really, why bother? I can replace this board completely with some AVR chips _and_ have room left over for a bunch of batteries.

The upper board seems to be just peripherals for the bottom board, all conveniently accessible through a 1×20-pin female header block.

There's a VFD Display with controller chip, a 4×4 button pad, a speaker, and a mag stripe reader. I expect to be able to control all of these through the header block.

The Controller Chip seems to be a simple serial shift-register controlled thing.

I expect the button pad will be a simple 4 row, 4 column matrix. I expect 8 of the pins on the header will be for the button pad.

I expect one of the pins will be to the piezo buzzer.

Probably one pin for the mag stripe reader too?

That leaves 5 pins unaccounted for.

Pin  1 - Row 1 of the keypad
Pin  2 - Row 2 of the keypad
Pin  3 - Row 3 of the keypad
Pin  4 - Row 4 of the keypad
Pin  5 - Column 4 of the keypad
Pin  6 - Column 3 of the keypad
Pin  7 - Column 2 of the keypad
Pin  8 - Column 1 of the keypad
Pin 13 - /POR on the OKI display chip.  Set this low for 
         200ns to reset the chip.
Pin 14 - DATA on the OKI display chip.
Pin 15 - SCLK on the OKI display chip.
Pin 16 - +5V for the board.
Pin 18 - Speaker
Pin 20 - GND for the board.

Thing thing has an awesome 16 character 16-segment VFD display with a OKI C1937-01 display driver.

It's a pretty standard shift register thing to get data into it, except that it reads DATA when SCLK goes _LOW_ instead of HIGH. Also, there's no LATCH. You have to be very careful about clocking it data, I guess?

To write to the display, you clock in “00” followed by 6 bits of value. 0x00 is ”@“. Actually, you can use ASCII values, sent through a “if (val > 63) val -= 64;” filter.

Power Consumption: OKI + VFD == 55-60mA

Okay, so I have a pretty simple API in place now..

• resetOki - Resets the controller IC
• setPosition - Sets the cursor to a certain position.
• writeChar - Takes an ASCII character, displays it on the screen.
• setBrightness - Sets the duty cycle (brightness).
• printString - A generic print that prints a series of letters on the screen.
• cyclon - Make a character go back and forth across the screen.

Still needed:

• Fade special effect (just calls setBrightness at a specified rate).
• Scroll special effect. Scroll a message across the screen at a specified rate and direction.

This looks like a standard matrix keypad. To read, you just activate the columns one by one, and see which (if any) of the row pins light up. Pins 1-8 of the header are the keypad.

Tie this to a timer interrupt, and you'll always have an uint16_t with the active buttons listed in it. (Er.. Overly complex. Just poll it when you need it.)

A Piezo Buzzer, connected to pin 18.

Man, NO idea. This is utter magic to me.

Is it a high and low value? Does it need an op-amp? There are a bunch of op-amps on the board. Maybe one of them?

How is data encoded?