Where are the pullups for the Commodore 64 keyboard matrix lines?6510 I/O port initialisationWhat use are the data direction registers in the MOS 6526 CIA?How to create a switchless multi-system 2 button Atari joystick?
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Where are the pullups for the Commodore 64 keyboard matrix lines?
6510 I/O port initialisationWhat use are the data direction registers in the MOS 6526 CIA?How to create a switchless multi-system 2 button Atari joystick?
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I'm looking at the schematic and the Service Manual for the Commodore 64. I can't seem to find a schematic for the keyboard itself.
It seems clear that the control port 1 joystick has normally open switches for the four directions and the fire button, and presses are detected by the switches closing and shorting lines COL0 through COL4 (connected to PA0 through PA4 on 6256 CIA U1) to ground, thus pulling them down to 0 V. So something must be pulling these lines up to +5 V when they're not shorted to ground.
Similarly, the description of keyboard scanning says that you drive one of COL0 through COL7 low and the rest high via output on PA0 through PA7, and then see which of ROW0 through ROW7 is brought low by a key in the matrix shorting one of those lines to the low COLn line, via reading PB0 through PB7. Again, this means that something must be pulling up ROW0 through ROW7 when they are not shorted to ground.
There are no pullup resistors for this in the motherboard schematic. The keyboard does have +5 V going to it; are there pullup resistors on the keyboard PCB?
commodore-64 mos-6526
asked May 30 at 8:00
Curt J. SampsonCurt J. Sampson
411110
add a comment |
I'm looking at the schematic and the Service Manual for the Commodore 64. I can't seem to find a schematic for the keyboard itself.
It seems clear that the control port 1 joystick has normally open switches for the four directions and the fire button, and presses are detected by the switches closing and shorting lines COL0 through COL4 (connected to PA0 through PA4 on 6256 CIA U1) to ground, thus pulling them down to 0 V. So something must be pulling these lines up to +5 V when they're not shorted to ground.
Similarly, the description of keyboard scanning says that you drive one of COL0 through COL7 low and the rest high via output on PA0 through PA7, and then see which of ROW0 through ROW7 is brought low by a key in the matrix shorting one of those lines to the low COLn line, via reading PB0 through PB7. Again, this means that something must be pulling up ROW0 through ROW7 when they are not shorted to ground.
There are no pullup resistors for this in the motherboard schematic. The keyboard does have +5 V going to it; are there pullup resistors on the keyboard PCB?
commodore-64 mos-6526
asked May 30 at 8:00
Curt J. SampsonCurt J. Sampson
411110
For more information on the pullups and their original purpose (not how they're used here) see answers to this question.
– Curt J. Sampson
Jun 1 at 3:22
add a comment |
I'm looking at the schematic and the Service Manual for the Commodore 64. I can't seem to find a schematic for the keyboard itself.
It seems clear that the control port 1 joystick has normally open switches for the four directions and the fire button, and presses are detected by the switches closing and shorting lines COL0 through COL4 (connected to PA0 through PA4 on 6256 CIA U1) to ground, thus pulling them down to 0 V. So something must be pulling these lines up to +5 V when they're not shorted to ground.
Similarly, the description of keyboard scanning says that you drive one of COL0 through COL7 low and the rest high via output on PA0 through PA7, and then see which of ROW0 through ROW7 is brought low by a key in the matrix shorting one of those lines to the low COLn line, via reading PB0 through PB7. Again, this means that something must be pulling up ROW0 through ROW7 when they are not shorted to ground.
There are no pullup resistors for this in the motherboard schematic. The keyboard does have +5 V going to it; are there pullup resistors on the keyboard PCB?
commodore-64 mos-6526
asked May 30 at 8:00
Curt J. SampsonCurt J. Sampson
411110
I'm looking at the schematic and the Service Manual for the Commodore 64. I can't seem to find a schematic for the keyboard itself.
It seems clear that the control port 1 joystick has normally open switches for the four directions and the fire button, and presses are detected by the switches closing and shorting lines COL0 through COL4 (connected to PA0 through PA4 on 6256 CIA U1) to ground, thus pulling them down to 0 V. So something must be pulling these lines up to +5 V when they're not shorted to ground.
Similarly, the description of keyboard scanning says that you drive one of COL0 through COL7 low and the rest high via output on PA0 through PA7, and then see which of ROW0 through ROW7 is brought low by a key in the matrix shorting one of those lines to the low COLn line, via reading PB0 through PB7. Again, this means that something must be pulling up ROW0 through ROW7 when they are not shorted to ground.
There are no pullup resistors for this in the motherboard schematic. The keyboard does have +5 V going to it; are there pullup resistors on the keyboard PCB?
commodore-64 mos-6526
commodore-64 mos-6526
asked May 30 at 8:00
Curt J. SampsonCurt J. Sampson
411110
asked May 30 at 8:00
Curt J. SampsonCurt J. Sampson
411110
edited May 30 at 23:37
Curt J. Sampson
asked May 30 at 8:00
Curt J. SampsonCurt J. Sampson
411110
asked May 30 at 8:00
Curt J. SampsonCurt J. Sampson
411110
asked May 30 at 8:00
Curt J. SampsonCurt J. Sampson
411110
411110
For more information on the pullups and their original purpose (not how they're used here) see answers to this question.
– Curt J. Sampson
Jun 1 at 3:22
add a comment |
For more information on the pullups and their original purpose (not how they're used here) see answers to this question.
– Curt J. Sampson
Jun 1 at 3:22
For more information on the pullups and their original purpose (not how they're used here) see answers to this question.
– Curt J. Sampson
Jun 1 at 3:22
For more information on the pullups and their original purpose (not how they're used here) see answers to this question.
– Curt J. Sampson
Jun 1 at 3:22
add a comment |
1 Answer
1
active
oldest
votes
No external pull-up is needed as the CIA already got internal circuitry to do so.
Port A and B have passive pull-up devices as well as active pull-ups
Taken from the CSG 6526 data sheet, section "I/O Ports" on page 5.
answered May 30 at 8:10
RaffzahnRaffzahn
60.7k6148249
add a comment |
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No external pull-up is needed as the CIA already got internal circuitry to do so.
Port A and B have passive pull-up devices as well as active pull-ups
Taken from the CSG 6526 data sheet, section "I/O Ports" on page 5.
answered May 30 at 8:10
RaffzahnRaffzahn
60.7k6148249
add a comment |
No external pull-up is needed as the CIA already got internal circuitry to do so.
Port A and B have passive pull-up devices as well as active pull-ups
Taken from the CSG 6526 data sheet, section "I/O Ports" on page 5.
answered May 30 at 8:10
RaffzahnRaffzahn
60.7k6148249
add a comment |
No external pull-up is needed as the CIA already got internal circuitry to do so.
Port A and B have passive pull-up devices as well as active pull-ups
Taken from the CSG 6526 data sheet, section "I/O Ports" on page 5.
answered May 30 at 8:10
RaffzahnRaffzahn
60.7k6148249
No external pull-up is needed as the CIA already got internal circuitry to do so.
Port A and B have passive pull-up devices as well as active pull-ups
Taken from the CSG 6526 data sheet, section "I/O Ports" on page 5.
answered May 30 at 8:10
RaffzahnRaffzahn
60.7k6148249
edited May 30 at 8:17
answered May 30 at 8:10
RaffzahnRaffzahn
60.7k6148249
answered May 30 at 8:10
RaffzahnRaffzahn
60.7k6148249
answered May 30 at 8:10
RaffzahnRaffzahn
60.7k6148249
60.7k6148249
add a comment |
add a comment |
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For more information on the pullups and their original purpose (not how they're used here) see answers to this question.
– Curt J. Sampson
Jun 1 at 3:22