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base:different_cpu_types [2015-04-17 04:31] (current)
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 +====== Different CPU types ======
 +
 +The Rockwell data booklet 29651N52 (technical information about R65C00 microprocessors,​ dated October 1984), lists the following differences between NMOS R6502 microprocessor and CMOS R65C00 family:
 +
 +<​code>​
 + 1. Indexed addressing across page boundary.
 +        NMOS: Extra read of invalid address.
 +        CMOS: Extra read of last instruction byte.
 +
 + 2. Execution of invalid op codes.
 +        NMOS: Some terminate only by reset. Results are undefined.
 +        CMOS: All are NOPs (reserved for future use).
 +
 + 3. Jump indirect, operand = XXFF.
 +        NMOS: Page address does not increment.
 +        CMOS: Page address increments and adds one additional cycle.
 +
 + 4. Read/​modify/​write instructions at effective address.
 +        NMOS: One read and two write cycles.
 +        CMOS: Two read and one write cycle.
 +
 + 5. Decimal flag.
 +        NMOS: Indeterminate after reset.
 +        CMOS: Initialized to binary mode (D=0) after reset and interrupts.
 +
 + 6. Flags after decimal operation.
 +        NMOS: Invalid N, V and Z flags.
 +        CMOS: Valid flag adds one additional cycle.
 +
 + 7. Interrupt after fetch of BRK instruction.
 +        NMOS: Interrupt vector is loaded, BRK vector is ignored.
 +        CMOS: BRK is executed, then interrupt is executed.
 +</​code>​
  
base/different_cpu_types.txt ยท Last modified: 2015-04-17 04:31 (external edit)