This daughter board provides a Composite Text video diplay output and has a PC keyboard input to allow for stand alone operation for the SBC-4 platforms.
The video is generated by an Atmel ATMega8 microcontroller. It's output is a standard analog NTSC composite video signal consisting of a 40 column by 25 line text display. Normal mode is white letters on a black background. Reverse mode is also available. This is a modified version of my original text display. It uses the AVR's internal SPI shift register to generate the pixel data, thus reducing the chip count.
The pc keyboard input is controlled by an Atmel ATTiny26 microcontroller. It converts the keyboard scan codes into ASCII characters for the host processor.
There is also a Lattice GAL16V8D programmable logic chip on the board that is used to gate the keyboard and video data to the right place at the right time and also provide the status signals to the host processor and the microcontrollers.
J2 is used to select one of the four I/O Device Selects. Jump Pins 1-2 for Device 1, 3-4 for Device 2, 5-6 for Device 3, or 7-8 for Device 4. Since IRQ's are not used on this board, no IRQ's need to be jumpered. However, R6 is provided to jumper 1 or more IRQ pins high to prevent unwanted IRQ's. IRQ1 is 9-10, IRQ2 is 11-12, IRQ3 is 13-14, and IRQ4 is 15-16. J5 is used to select NTSC (1-2) or PAL (2-3) video generation. PAL mode is untested (I do not have a PAL TV anymore), but should work.
User input and output can be re-directed to the Term board, allowing independent operation and control without the need for a PC connected to the Serial port.
Here is a schematic of this board: