2 Oct
2007
2 Oct
'07
1:17 p.m.
woodelf wrote:
Yes thats true. Fortunately the address bus was not munged up but all
the registers and the pointers they form are 16bit so a split bus slowed
things some due to the limitations of ram speed. What was done was at the
point in the processor read, write or RMW cycle they would insert a wait
and then mux/demux the bus depending on direction. The overall cost was
around two wait states due to ram speed rather than CPU speed. Since the
bus splitting was done outside the CPU it was less costly then the 9080
flavor.
Actually the 9900 was a fine chip and there were faster versions never
really got marketed. It was the first real 16bitter.
Allison
> The 9900 chips is not crippled, for 1976
three voltage NMOS its about
> as fast
> as the technology of the time could go. The TI99/4 did however do a
> nasty to
> it. One is they muxed the bus down to 8bits wide and that does slow
> the system
> some. There were 128 words of ram (6810s) that if you execute there
> the speed
> is noticeable.
If I remember right, the architecure of the ti chip
it used a pointer to ram as the internal registers. That would really
bog down on byte wide bus. The year sounds right as
I remember BYTE talking about the chip. One of the few times
you had BYTE not looking at 8080/Z80 cpu's.
Ben.