5 Mar
2010
5 Mar
'10
4:25 p.m.
> Nope, not gonna take it back.
> In my circle of users in Brooklyn, EVERYBODY with a Model I had a
> doubler if they had disk drives. EVERYBODY.
On Thu, 4 Mar 2010, Tony Duell wrote:
It is extremely unscientific to stick to a
statement when you have clear
evidence to the contrary.
I haven't seen any clear evidence that he every hung out with anybody
without a doubler, so his statement could be technically true. > and had lots of trouble reading disks.
Among the people that _I_ hung out with, everybody had already solved that
long before the doubler became available.
This is soemthing I can't explain. I have a
'stock' M1 EI, using the
internal data separator of the 1771. I never had _any_ problems with it.
It read disks with no isseus at all. I had many more problems with the M3
(first of all that infernal tapewire cable between the CPU board and the
disk controller board, and in fact I had to replace the 1793 chip in the
M3 at least once). Oh well...
I wonder if there were any differences in the Expansion Interface, other
than the power supply?
Around here, there were lots of EI problems unrelated to the FDC.
RS did a "free" "upgrade" of EIs to a "buffered cable"
between the CPU and
the EI, then did an "upgrade" to add an additional DIN cabel, then another
"upgrade" which included switching back to an unbuffered cable.
This all relates to the DRAM timiog. The DRAM system needs 3 accurately
timed signals, RAS/, cAS/ and Mux (this being the control input to the
address multiplexer). They are all produced and used on the M1 processor
board for the intenral DRAM. ANd they were brought out to the expansion
connector.
The original intention was to feed those along a ribbon cable to the EI.
This AFAIK never worked propperly. The next idea was to fit a buffer PCB
in the calbe ot clean up those signals. Then to use a screned DIN cable
to carry them. And findally to only use the RAS/ signal from the M1 CPU
board and to geenrate the other 2 signals inside the EI using a delay line.
My EI is one of the last design. I have just dug out the scheamtics that
came with it, and from waht I can see there were no changes to the disk
cotnroller section. Thre is no external data separator, the XTDS/ pin of
the 1771 is pulled high (this pin is low if you have an external data
separator and high to use the one built into the 1771 I think).
-tony