The Channel F console used the Fairchild F8 processor running at the color burst frequency divided by 2 (1.79MHz) and had 2 program storage units (that processor's equivalent to ROM), giving it a 2K BIOS that contained the built-in games Hockey and Tennis as well as some subroutines other carts could use. The F8 CPU has 64 scratchpad registers, so there was no RAM, except for the 8K x 2 bits for its 128 x 64 pixel screen (not all the pixels were visible). The 2 bits per pixel gave 4 colors, but it used a trick to change between 4 palettes that gave a total of 8 colors. By storing different values in pixels 125 and 126, one of 4 different palettes could be chosen for each line.
The CPU and one of the PSUs also had two 8-bit I/O ports. The CPU ports were connected to the 4 buttons on the console and to the right hand controller. 3 of the lines were used to write to screen RAM. The PSU's ports were connected to the left hand controller, the screen RAM and the sound hardware.
To plot a point on the screen, you'd output the row, the column, the color and then set a bit to perform the write. You could make 3 sounds- a 500Hz beep, a 1KHz beep or a 120Hz beep.
The original System I board used discrete TTL chips, while the System II board used VLSI. The System II had a slight change to the sound hardware that allowed the programmer to rapidly toggle the sound on and off to produce other frequencies, like the Pro Football songs. These notes sound terrible on a System I console. System I had a built-in speaker (no volume control), while System II sent the audio to the TV.
Carts typically held two PSUs, for 2K of ROM space. Some notable exceptions are Maze and Hangman, which also had a 2102 SRAM connected to the cart PSU's I/O ports. Some of the later games were larger at 3K or 4K, and the German Saba Schach (Chess) cart was 6K. The 4K carts used an F3853 Static Memory Interface and a 4K ROM, while the Schach cart had 2 ROM chips and 2K of 8-bit RAM.
The cart pinout is as follows:
1 ground 2 ground 3 D0 4 D1 5 /INTREQ 6 ROMC0 7 ROMC1 8 ROMC2 9 D2 10 ROMC3 11 D3 12 ROMC4 13 PHI 14 D4 15 WRITE 16 D5 17 D6 18 D7 19 +5V 20 +5V 21 unused 22 +12V
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