Support chips

Support chips

* 4001: 256-byte ROM (256 8-bit program instructions), and one built-in 4-bit I/O port
* 4002: 40-byte RAM (80 4-bit data words), and one built-in 4-bit output port; the RAM portion of the chip is organized into four "registers" of twenty 4-bit words:
o 16 data words (used for mantissa digits in the original calculator design)
o 4 status words (used for exponent digits and signs in the original calculator design)
* 4003: 10-bit parallel output shift register for scanning keyboards, displays, printers, etc.
* 4008: 8-bit address latch for access to standard memory chips, and one built-in 4-bit chip select and I/O port
* 4009: program and I/O access converter to standard memory and I/O chips
* 4269: keyboard/display interface
* 4289: memory interface (combines functions of 4008 and 4009)