| TTL Oscillator Design Questions [message #7219] |
Tue, 10 March 2020 14:15  |
protocall7
Messages: 20
Registered: October 2019
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Junior Member |
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Hi All,
I am working on a Z80 design, and have been messing around with these full-can TTL oscillators that fit in a 14-pin DIP socket from Jameco:
https://www.jameco.com/z/OSC4-4-MHz-Full-Can-Crystal-Oscilla tor_27967.html
They seem to work great by themselves in the breadboard, but I am getting closer to a final design, and the info Jameco provides is almost nonexistent. I was wondering if anyone could help me with a couple things that have been bothering me:
1) Should these have any pull-up/pull-down resistance on the output?
2) Do these require a decoupling cap across VCC/GND?
3) These don't require any load capacitance like a quartz crystal would, do they? (I assume not since I've been using them without for a while now without issue, but figured I'd ask in case I'm just getting lucky with breadboard capacitance)
Thanks!
Peter
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| Re: TTL Oscillator Design Questions [message #7220 is a reply to message #7219] |
Tue, 10 March 2020 14:24  |
jcoffman
Messages: 332
Registered: October 2015
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Senior Member |
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Peter,
Most of the 14-pin (and 8-pin) size oscillators are CMOS level outputs. They may be used in CMOS and TTL designs. They need NO external components.
Pin assignments are 7-GND, 8-output, 14-VCC. Newer oscillators have an on/off capability on pin 1: GND==off, VCC==on. However, they have internal pull-up resistors on pin 1 so that they may be used in circuits that do not connect pin 1. Hence, all oscillators are created equal, unless you want to use this on/off capability. I never have.
The 8-pin cans are similar: pin are: 4-GND, 5-output, 8-VCC. Newer ones will also have the internal pull-up on pin 1.
--John
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| Re: TTL Oscillator Design Questions [message #7221 is a reply to message #7219] |
Tue, 10 March 2020 14:29 |
Sergey
Messages: 238
Registered: October 2015
Location: Portland, OR
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Senior Member |
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protocall7 wrote on Tue, 10 March 2020 14:15Hi All,
I am working on a Z80 design, and have been messing around with these full-can TTL oscillators that fit in a 14-pin DIP socket from Jameco:
https://www.jameco.com/z/OSC4-4-MHz-Full-Can-Crystal-Oscilla tor_27967.html
They seem to work great by themselves in the breadboard, but I am getting closer to a final design, and the info Jameco provides is almost nonexistent.
That's why I almost completely stopped using Jameco... Their prices are not better than Mouser/DigiKey, but you never know what are you getting...
Quote:
I was wondering if anyone could help me with a couple things that have been bothering me:
1) Should these have any pull-up/pull-down resistance on the output?
Probably not. While Z80 needs a higher than normal TTL logic HIGH level, I never had a problem with that. If unsure, install a 4.7k pull-up resistor... Another way around is to purchase CMOS oscillators ;-)
Quote:
2) Do these require a decoupling cap across VCC/GND?
It is a good practice to have 0.1 uF capacitor on every logic IC (maybe on every two) including oscillators. It should connected with as short traces as possible to VCC and GND pins.
Quote:
3) These don't require any load capacitance like a quartz crystal would, do they? (I assume not since I've been using them without for a while now without issue, but figured I'd ask in case I'm just getting lucky with breadboard capacitance)
No they don't requite a load capacitance. They have an integrated crystal and an oscillator IC, and everything else to make the oscillator work.
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