RCA1802

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CPU RCA1802

The Radio Corporation of America (RCA) introduced in 1974 the RCA in 1802 as the first CMOS - microprocessor on the market. It can be operated with an operating voltage of up to 10 V and a maximum clock frequency of 6.4 MHz, with lower voltages correspondingly less. The internal structure and the commands are kept very simple.

Applications

Right from the start, the 1802 was also manufactured as a silicon-on-sapphire variant. This design gave the microprocessor a certain degree of resistance to ionizing radiation and electrostatic discharge . At the same time, the leakage currents decrease so that you can work with significantly lower power consumption. This, combined with its ability to operate at extremely low voltages, made the 1802 extremely suitable for space travel. In addition, there were very few processors on the market at the time that were similarly insensitive to radiation. The 1802 was a popular microprocessor for many satellites and was e.g. B. used in the Galileo mission of NASA and the OSCAR amateur radio satellites of AMSAT . It was also widely used in military technology , which explains its production, which continues to this day.

A number of micro-computers based on the 1802, including the COSMAC ELF , COSMAC VIP , ELF II , SuperELF and Yugoslav Pecom 32 , as well as the RCA Studio II - game console . In the world of chess computers , the 1802 was used in the early 1980s in the Mephisto I , II and III from the Munich electronics manufacturer Hegener + Glaser .

Internal structure

Data bus width 8 bits, address bus width 16 bits multiplexed, seven I / O addresses

In addition to the accumulator, the processor has sixteen 16-bit registers that can also be used eight-bit. There are two registers (X, P) with four bits that determine which of the 16-bit registers work as data pointers and program counters. There is only one carry flag for the battery. A zero flag is not required. There is an output signal that can be set by program. Four EF lines can be queried via the program. The address bus is multiplexed as eight bits twice. The cycle time is one eighth of the clock frequency. Almost all commands require two, only a few three cycles.

Command structure

The simple structure of the hardware continues with the program commands.

So it takes z. B. four commands to load one of the 16 registers: 

-----------------------------------------------------------------------------------------
  LDI      n1      ; LOAD IMMEDIATE  1. Byte in den Akku
  PLO      1       ; PUT LOW  den Akkuinhalt in das niederwertige Byte des Registers R1
  LDI      n2      ; LOAD IMMEDIATE  2. Byte in den Akku
  PHI      1       ; PUT HIGH  den Akkuinhalt in das höherwertige Byte des Registers R1

There are also jump instructions that only need two cycles and two bytes, but whose destination must lie within the same page, i.e. H. the higher eight bits of the address must not change. There is no direct subroutine call (CALL), a similar function can be achieved by changing the program counter.

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