5½" x 2" (14 x 5.1cm) piece of thin
aluminum; ¾" x 3/8" (19.1 x 9.5 cm) pine
for chassis rails; 14-pin IC sockets (4);
16-pin IC sockets (3); 22-pin IC sockets
(2); 40-pin IC socket; connector for
power supply; 9-volt, 350-mA dc power
source; 1¼" x ¾" x 1/8" (31.8 x 19.1 x
3.2 mm) piece of aluminum; dry-transfer
lettering kit; machine and wood
hardware; hookup wire; solder; etc.
Note: the CDP1802 COSMAC microprocessor chip is available from any RCA parts distributor as is the COSMAC user manual.
automatically incremented so that it points to the next instruction to be fetched. Branch instructions can be used to change the address in the program counter to permit jumping (branching) to a different part of the program when desired. The digit in the 4-bit P register specifies which 16-bit general-purpose register is being used as the program counter.
Timing Sequence. Since many of the 1802 microprocessor's instructions are only one-byte long and require two machine cycles, the first cycle is always an instruction fetch, or memory read. The fetched instruction is executed during the next machine cycle, which could be a memory-read memory-write, or register-transfer type of cycle.
Program execution always consists of a sequence of fetch-execute cycles, and the two SC0 and SC1 lines (see Fig. 4 and Fig. 5) indicate what type of cycle is being performed according to the following criteria:
|SC1||SC0||Type of Machine Cycle|
Circuit timing is shown in Fig. 6.