13 Apr
2005
13 Apr
'05
10:23 p.m.
(not gonna wire two 6402 UARTS to my SYM-1 and [...])
How about one Z8530? :-) [it's a DUART, for the Zilog-impaired] I am thinking that it's the serial chip in the
Sparcstations, correct
me if I'm wrong.
No, that's right as far as it goes - most SPARCstations, at least.
A few years ago I was pondering making a 'dialup
connecting system
with NAT server' out of a SparcStation Classic (the little lunchbox
type Sparc).
Well, _one_ of the lunchbox SPARCs. (The others are the IPC, the IPX,
and the LX.)
I discovered quickly that the serial ports on the
Sparc are VERY
speed constrained because of the 8530 chip. It would have been
impossible to connect my USB Courier V-everything modem to it at, say
57,600 baud, because the 8530 just plain won't go that fast.
While this is true of the 8530 *as used in the SPARCstations*, this is
largely because of the clock Sun chose to drive it with. Use a faster
clock and your baud rate cap goes up correspondingly. (Presumably
there is a limit on the clock rate, but I don't know what it is; I'm
fairly sure it's well above what Sun uses, at least.)
Now, depending on the associated electronics, there may be other
limits. For example, the 8530 has discouragingly little buffering
on-chip; to run at high baud rates you will need to either (a) add
buffering in front of it, (b) handle a relatively high rate of
interrupts, or (c) do some rather delicate bare-metal tapdancing.
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