General Instrument CP1600

Honeywell used the CP1600 in a number of process control computers and related systems, but its most widespread use was the CP1610 version in the Intellivision video game console.

[3] The CP1600 was implemented in enhancement mode nMOS and required +12, +5, and −3 V power supplies; I/O connections except for the clocks were TTL (5 V) compatible.

Due to the voltage requirements of the clock signals, these had to be generated with external circuitry, as was common in this era of microprocessor design.

[3] In order to fit a 16-bit processor into a 40-pin dual in-line package (DIP) chip design, the CP1600 multiplexed its data and address pins.

This allowed a set of 16 pins to be used for both address selection and reading and writing data, but to do so required two bus cycles.

It also complicated the overall machine layout as buffers were required on the memory bus to latch the address while the processor switched the pins to data mode.

The interface to the system was likewise complex, requiring three pins, BDIR, BC1 and BC2, which had to be decoded to understand what state the memory bus was in.

As data and addresses would still require 16-bit values, the 1600 included a special SDBD instruction that pieced together a 16-bit argument from two 10-bit ROM reads.

Early documentation shows two planned chips in the series, the 1616 which added the "Extended Instruction Set", and the 1618 "Priority Expander".

This meant that implementations had to use latches or buffers to be able to interface with the CPU as it changed the bus from indicating an address to data.

To address this problem, GI supplied a series of 164x dedicated I/O chips that implemented the required bus logic.

As with the other 1640 series chips, the PIC internally decoded the bus logic, but also added a very simple processor that could run its own programs to perform I/O and direct memory access.