10 Feb
2022
10 Feb
'22
9:50 p.m.
I've got a piece of gear here with a bad MC858P used as a bus
driver--terminated in 220/330 ohms at the far end.
Given that old DTL is a hit-or-miss proposition, I'm proposing to
substitute a 7438 OC buffer. Pinout's the same, as is Vcc.
Before I get out the soldering iron, any "don't do it" thoughts?
--Chuck
10 Feb
10 Feb
10:39 p.m.
On 2022-Feb-10, at 9:50 PM, Chuck Guzis via cctalk wrote:
I've got a piece of gear here with a bad MC858P
used as a bus
driver--terminated in 220/330 ohms at the far end.
Given that old DTL is a hit-or-miss proposition, I'm proposing to
substitute a 7438 OC buffer. Pinout's the same, as is Vcc.
Before I get out the soldering iron, any "don't do it" thoughts?
Are you sure the pinouts match? The Moto book I'm looking at indicates the 858 gates
are 'pointing to the middle' (outputs:3,4,10,11) in contrast to the 7438 common
'all gates pointing to the right' (outputs:3,6,8,11).
I've replaced DTL with TTL on occasion or two in the past. They're both
current-sinking logic so they work together well enough as far as output-input drive.
11 Feb
11 Feb
9:59 a.m.
On 2/10/22 22:39, Brent Hilpert wrote:
On 2022-Feb-10, at 9:50 PM, Chuck Guzis via cctalk
wrote:
Close enough--using an SOIC-to-DIP breakout board, swap pins 8-10 and
6-4 and Bob should be your uncle. Use 7438 SOIC, of course.
At least I believe that should work. Prices for NOS DTL are
predictably crazy.
--Chuck
I've got a piece of gear here with a bad
MC858P used as a bus
driver--terminated in 220/330 ohms at the far end.
Given that old DTL is a hit-or-miss proposition, I'm proposing to
substitute a 7438 OC buffer. Pinout's the same, as is Vcc.
Before I get out the soldering iron, any "don't do it" thoughts?
Are you sure the pinouts match? The Moto book I'm looking at indicates the 858 gates
are 'pointing to the middle' (outputs:3,4,10,11) in contrast to the 7438 common
'all gates pointing to the right' (outputs:3,6,8,11).
I've replaced DTL with TTL on occasion or two in the past. They're both
current-sinking logic so they work together well enough as far as output-input drive.
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