Another consideration with the TC02 is the small buffer. I don't know
what tape speed your drive runs at, but we lost a lot of sales to Dilog
because of buffer overflow on some of the faster CDC dirves. When we
came out with the TC03, it had a larger buffer to handle this.
cheers,
Nigel Johnson
On 12/08/2019 11:13, Jon Elson via cctech wrote:
On 08/11/2019 08:00 PM, Douglas Taylor via cctech wrote:
This is where the electrical engineer could help. How do you
determine how long a cable the 74LS240 can drive?
Well, there are several considerations. First, it takes some current
to charge up the cable capacitance. More current charges the
capacitance faster, but also creates faster edges which cause more
crosstalk. Then, the data rate needs to be considered. Mag tape data
rates are not that high. So, for 1600 BPI at 45 IPS, the data rate is
72 K bytes/second, or about 14 us per byte.
Twisted-pair cable should have a little less capacitance, and it is
supposed to reduce crosstalk, so should work better.
The most serious problem is when many data lines switch at the same
time, it may contaminate the clock pulses and cause bytes to be
dropped or added.
With the low data rates involved, proper delays to allow ringing to
settle on the data lines and prevent short crosstalk pulses from
affecting the clocks should make the system very tolerant of cable
issues. But, maybe some engineers didn't really optimize their logic
for these problems.
Jon
--
Nigel Johnson
MSc., MIEEE
VE3ID/G4AJQ/VA3MCU
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