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Lexikon

RCA 1802

An extremely simple href="module.php?name=Lexikon&file=search&eid=1&query=microprocessor">microprocessor fabricated in href="module.php?name=Lexikon&file=search&eid=1&query=CMOS">CMOS, running at 6.4 Mhz at 10V (very fast for 1974). It could be suspended with the clock stopped. It was an 8-bit processor, with 16-bit addressing. Simplicity was the primary design goal, and in that sense it was one of the first href="module.php?name=Lexikon&file=search&eid=1&query=RISC">RISC chips. It had sixteen 16-bit href="module.php?name=Lexikon&file=search&eid=1&query=registers">registers, which could be accessed as thirty-two 8-bit registers, and an href="module.php?name=Lexikon&file=search&eid=1&query=accumulator">accumulator D used for arithmetic and memory access - memory to D, then D to registers and vice versa, using one 16-bit register as an address. This led to one person describing the 1802 as having 32 bytes of href="module.php?name=Lexikon&file=search&eid=1&query=RAM">RAM and 65535 I/O ports. A 4-bit control register P selected any one general register as the {program counter}, while control registers X and N selected registers for I/O Index and the operand for the current instruction. All instructions were 8 bits - a 4-bit href="module.php?name=Lexikon&file=search&eid=1&query=op code">op code (total of 16 operations) and 4-bit href="module.php?name=Lexikon&file=search&eid=1&query=operand register">operand register stored in N. There was no real href="module.php?name=Lexikon&file=search&eid=1&query=conditional branching">conditional branching, no href="module.php?name=Lexikon&file=search&eid=1&query=subroutine">subroutine support and no actual href="module.php?name=Lexikon&file=search&eid=1&query=stack">stack but these could be implemented by clever use of registers, e.g. changing P to another register allowed jump to a subroutine. Similarly, on an interrupt P and X were saved, then R1 and R2 were selected for P and X until an href="module.php?name=Lexikon&file=search&eid=1&query=RTI">RTI restored them. The href="module.php?name=Lexikon&file=search&eid=1&query=RCA 1805">RCA 1805 was an enhanced version. The 1802 was used in the href="module.php?name=Lexikon&file=search&eid=1&query=COSMAC">COSMAC (VIP?) href="module.php?name=Lexikon&file=search&eid=1&query=microcomputer">microcomputer kit, some video games from href="module.php?name=Lexikon&file=search&eid=1&query=RCA">RCA and href="module.php?name=Lexikon&file=search&eid=1&query=Radio Shack">Radio Shack, and the href="module.php?name=Lexikon&file=search&eid=1&query=ETI-660">ETI-660 computer. It was chosen for the Voyager, Viking and Galileo space probes as it was also fabricated in {Silicon on Sapphire}, giving radiation and static resistance, ideal for space operation. href="http://www.cosmacelf.com">More history . (2002-04-09)

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