"Jasen Betts" wrote to "Greg Mayman" (20 Dec 02  18:54:07)
 --- on the topic of "THOSE OLD EXPENSIVE [1/2]"

 GM> And they still managed to keep the instruction set a lot simpler
 GM> than the Z80 ;-)

 JB> Which had A,B,C,D,E,H,L registers (also avalialbe 16 bit BC DE HL) and
 JB> 8 bits of flags, and a nother set just like it,  then 2 16 bit index
 JB> registers, 16 bit IP and SP registers, an 8 bit refresh regiter that
 JB> incremented on every clock cycle,

The refresh counter was only 7 bits wide. (& don't recall why!)


 JB> The registers weren't all interchangable though. for some things only
 JB> one register could be used.

The pain with the 8080 and z80 was that though it had a lot of registers
most tended to be specialized for specific tasks. The 65xx and 68xx
internal registers tended to be more general purpose, though there were
fewer it could use a page of memory as a bunch of registers. The z80 had
a lot more internal registers among which was a second duplicate set
which could be switched to back and forth. It was great since one didn't
have to save the machine state on the stack, for example the response to
an interrupt and the return were very fast indeed with a single
instruction used for switching to the alternate register set.

 Mike
 ****

... That was a fascinating period of time for electronics
--- Blue Wave/DOS v2.30