Pertec Interface Cable Length
nw.johnson at ieee.org
Mon Aug 12 10:16:20 CDT 2019
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.
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.
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