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ready.
Registered: Feb 2003
Posts: 441 |
C64 ports 5V supply max current rating
What is the reson behind having different current ratings at user port (max 100mA) and expansion port (max 450mA)? Ratings are from the programmer's reference guide. I thought it is strange to have different ratings since they should both come from the same 5V line.
My problem comes from a card I am building for user port which will need more than 100mA current. What is the rating of the cassette port 5V line supply? I couldn't find it anywhere. |
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chatGPZ
Registered: Dec 2001
Posts: 11499 |
where did you find that 450mA figure? in my c64 manual it says 100mA everywhere (user port, joystick ports).... it doesnt say anything about exp.port though :) |
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ready.
Registered: Feb 2003
Posts: 441 |
here for example, page 366:
http://www.commodore.ca/manuals/c64_programmers_reference/c64-p..
I am sure anyhow that exp port can handle more than 100mA since I have been using for quite a long time an interface with optos which draws at least 200mA. |
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chatGPZ
Registered: Dec 2001
Posts: 11499 |
it says "TOTAL user port and cartridge devices can draw no more than 450mA" ... it doesnt say anything about what you can draw from each +5 pin at the expansion port all unfortunately (i'd still assume its ~100mA like other pins on other ports) |
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ready.
Registered: Feb 2003
Posts: 441 |
true, you are correct, the global USER PORT + EXP PORT is specified. Still I wonder why the USER PORT +5V pin is limited to 100mA. The only thing which comes to my mind is that the USER PORT +5V pin is further away from the inlet power connector, thus the path "power connector - USER PORT" has higher impedence than path "power connector - EXP PORT", and high current consumption might cause too high voltage drop affecting other circuits operation. But I don't see any danger in burning anything if the USER PORT delivers more than 100mA, provided the power supply can handle it. Or should I worry about this? |
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chatGPZ
Registered: Dec 2001
Posts: 11499 |
the traces on the board may not have the required thick/wideness to deliver more than that. or the pins at the port. |
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ready.
Registered: Feb 2003
Posts: 441 |
yes, that was my idea as well. |
