!pr2
65C02 Department....................................Bill Morgan

I am holding a brand new NCR65C02A.  Now I finally believe that there is such a creature as a 65C02!  NCR's version of this processor seems to be the same as GTE's.  That is, it has all of the enhancements described in the December '82 issue of AAL, except for the single bit set, reset and branch instructions.

We have tested the chip in the computers here, and there's good news and bad news.  As Don Lancaster reported last month, the new chip works perfectly in an Apple //e.  You just swap processors and start using new opcodes.  However, 65C02 chips do not work in the Apple ][ or Apple ][+.

I am told that the problem lies in the execution of instructions like ASL or INC, which read memory, modify the contents, and write the result back to the same address.  The 6502 processor does one read and two writes during such an instruction, which is really incorrect.  In the 65C02 this has been changed to the proper combination of two reads and one write.

Unfortunately, the Apple ][s rely on the timing of the read-write-write cycle, and the read-read-write cycle is just different enough to cause the system to fail.  Hopefully some of the hardware specialists can come up with a modification to the older Apples to allow the use of the enhanced processors.

Let's talk about programming the 65C02.  With the new chip in a //e, Bob and I started tearing into the S-C Word Processor.  We just went through the code, looking for places to substitute a new instruction for several old ones.  Come to find out, the most useful change is the true Indirect addressing mode, in place of Indexed Indirect.  That means replacing

     STY YSAVE
     LDY #0
     LDA (POINTER),Y
     LDY YSAVE          with     LDA (POINTER).

That's replacing 8 bytes with 2 bytes.  BRA (BRanch Always) and STZ (STore Zero) also came in very handy.

All things considered, Bob has decided to wait for the Rockwell version of the 65C02, because he really wants those single bit set, reset, and branch instructions.  At last word Rockwell was expecting to start shipping in August, so it will be at least that long before we have any.  NCR's chip costs about $10.  The Rockwell chip may cost a little more, if and when.  We have noticed ads offering 65C02's for $35, which just goes to show how expensive advertising can be.
