11 Aug
2011
11 Aug
'11
1:52 p.m.
On 11 Aug 2011 at 20:08, Tony Duell wrote:
I have noi idea of the cost of an 8089 at the time,
but th esupport
circuity would have been a lot less than that needed by the 8237 (no
pag register and associated logic). Yes, you'd have needed some memory
refresh hardware, but countless other machines provided that without
needed a DMA channel to do it (and you didn't _have_ to used a
single-chip DRAM controller). Remmber that in the PC, all the DMAC did
for the RAM was the refresh operation, the timing of RAS/CAS, addres
multiplexing, etc was done in separate hardware. Adding a refresh
counter and th eassociated logic would npt have been that much exta.
Looking back at the 8089 datasheet, I'm not convinced that it
provides much for the money. In the minimum-component "local" mode,
it executes out of the 808x CPU memory space, being another contender
for that resource. At 5MHz with no contention/interleaving it can
transfer a byte every microsecond, best case--not much better than an
8237.
The bean counters would not have been happy.
--Chuck