Here you will find all the information and links that I have on this interesting little display. This page gives a basic overview of the display. There are additional pages showing the fonts available and some sample displays.
This display module was manufactured by Hyundai (Part Number HG12603-A) for AT&T. It measures 137mm wide x 90mm high x 20mm deep with a viewable display area of 110mm x 58mm. It's main claim to fame is that it is the LCD used by the PJRC 8051 MP3 player.
The front of the display module consists of an 8 row x 24 character LCD panel, an LCD contrast adjustment slider pot at the top and a red LED at the lower right hand corner.
The rear of the display module has an 80C32 microcontroller (IC3) clocked at 11.0592 MHz, 64Kb RAM (ICs 7 & 8), a socketed PROM (IC9) and several miscellaneous support chips. The actual display is driven by two Samsung KS0108B dot matrix LCD controllers (hidden beneath the LCD panel), one for the left hand 12 columns and one for the right hand 12 columns. The KS0108B is a graphical controller but unfortunately the actual LCD pixels are grouped in 5x8 blocks making the display unsuitable for bitmap graphics.
Depending on which display you have, IC9 will either be the original AT&T PROM or an AMD AM29F010B FLASH device. If you have a 29F010B then chances are your board has been programmed with the PJRC firmware and fonts. If you still have the AT&T PROM, then you need to remove it and replace it with a 29F010B with the PJRC firmware.
With the PJRC firmware installed, the display module supports several commands. The details of these commands can be found on the PJRC web site. I've listed most of the commands here but without the detail.
The interface to the outside world is via a 17 pin connector on the left hand side (J100). Pin 1 is indicated by a small arrow on the top of the connector nearest the top of the board. The connector pinout is detailed on several sites around the net and I've also detailed it here. The pins in bold are required to use the display in it's most basic mode. Pin 1 is required if you want to receive anything back from the display. The rest are optional but potentially very useful.
| Pin Number | Description |
| 1 | TTL RS-232 Transmit Data from the 80C32 at 19200,8,N,1 |
| 2 | 80C32 Port pin P3.2 |
| 3 | TTL RS-232 Receive Data to the 80C32 at 19200,8,N,1 |
| 4 | 80C32 Port pin P1.3 |
| 5 | 80C32 Port pin P1.2 |
| 6 | 0v |
| 7 | 80C32 Port pin P1.4 |
| 8 | ? |
| 9 | Pin 18 of PAL |
| 10 | 80C32 Port pin P3.3 |
| 11 | 80C32 Port pin P1.7 |
| 12 | Reset Input |
| 13 | 80C32 Port pin P1.0 |
| 14 | 0v |
| 15 | +5v DC in |
| 16 | +5v DC in |
| 17 | -9v DC in for display |
It is important to note that the serial I/O of the board is at TTL level and therefore needs to be level shifted to work correctly with a standard RS-232 serial port.
I have a daughter board with a MAXIM MAX232 line driver IC and associated components connected to the rear of the LCD module. The daughter board also breaks out all the additional signals. A simple 4 pin connector with 0v, +5v, TxD and RxD is all that is required to communicate with the display.
The above image shows the daughter board attached to the display board with the 4 pin connector visible. The 4 pin connector is a standard 0.1" pitch 4 way 90 degree header. The connections to the 4 pin connector are as follows:
| Pin Number | Description |
| 1 | 0v DC |
| 2 | RS-232 Rx Data (i.e. commands from the host to the LCD) |
| 3 | RS-232 Tx Data (i.e. responses from the LCD to the host) |
| 4 | +5v DC regulated unprotected |
Pin 1 is the pin closest to the 17 way connector (J100). The pin numbers run left to right in the picture above with pin 1 on the left.
Note that there is no reverse polarity protection or over voltage protection on this module. Check very carefully your voltages before connecting power to the display.