From: Wolfgang Moser (womo_at_news.trikaliotis.net)
Date: 2008-11-08 09:29:20
Hello Jim,
Jim Brain schrieb:
> [...]
> As to your inquiry about not being able to drive a 1541 from the AVR, I
> wonder if the AVR cannot sink enough current to overcome the 1KOhm
> pullups in the 1541. It would not be my first thought, but aside from
> protocol concerns, one must consider the electrical portion of the bus.
the MMC2IEC and Shadowwolf's redesign MMC2IEC 1.6 did work
fine without extra amplifiers as long as only one IEC bus
device was connected to the MMC2IEC and no speeder protocols
were used.
I remember that Shadowwolf and I came into a discussion (via
private mail, not the german Forum-64), when users started
to report to him some slight transfer errors, when either
more devices than a C64 and a 1541 were connected to the IEC
bus or the speeder protocols were used.
I told him about the construction of the XA1541 cable and
the long history about finding and measureing the right
transistor types to serve the IEC bus in the best way.
In the end, if you want to prevent yourself and your
customers from too many support sessions, I strongly
recommend to spend some extra drivers to drive the IEC bus.
Taking some digital switching MOSFETs like the BS170,
2N7000 or 2N7002 would enable the µIEC to securly drive
more than 5 devices on the IEC bus (C64 plus 4 devices),
even when fast speeder protocols are used that require
low falling times (IEC bus line getting active).
Shadowwolf populated his SD2IEC 1.2 with even stronger
HEXFET MOSFET transistors, because he had to do the 3.0V
to 5.0V voltage conversion additionally.
Womo
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