fa42e8c377
git-svn-id: https://svn.salfter.gotdns.org/svn/a2bfc/trunk@93 1b90f75b-8b96-4784-87c0-14078182fce6
76 lines
3.7 KiB
Plaintext
76 lines
3.7 KiB
Plaintext
Connecting 1-Wire devices to your Apple II is dead simple. A 74HCT126 quad
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three-state buffer, a 4.7k resistor, a 0.1uF capacitor, and the appropriate
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connector to plug into the 16-pin joystick port is all you need. (The 9-pin
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joystick port on the IIe and later machines is inadequate for our purposes
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since it has no outputs.) The circuit looks something like this:
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+5V o--------------+-------| C1 |-----o GND
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| | 0.1uF |
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AN0 o-------| / +-----|(-----+
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| \ R1 | |
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| / 4.7k v U1 v
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|\| \ Vdd 74HCT126 Vss
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| \ |
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GND o-----| >-----+------+----------------------------------o to 1-Wire bus
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| / |
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|/ U1A |
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| GND o--+---+---------+---|
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+5V o------| | | | | |
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|/| | | |\| | |\|
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/ | | | | \ | | \
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PB2 o-----< |------------| |-| > |-| >
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\ | | / | /
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\| U1B |/ U1C |/ U1D
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We use four signals on the joystick connector:
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+5V (pin 1) 5V power supply
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GND (pin 8) system ground
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AN0 (pin 15) annunciator 0 output
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PB2 (pin 4) pushbutton 2 input
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Something similar to DigiKey part # CDP16G-ND would be a suitable connector
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to plug into the joystick connector, with a ribbon cable leading away to a
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breadboard or an external enclosure for the circuit. If you built the
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circuit on a PC board for in-computer installation, a 16-pin wire-wrap
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socket would work (and would allow passthrough connection of a joystick or
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paddles). To wire up the circuit on a breadboard, use this list of
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connections:
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- pin 1 of the joystick connector to one end of R1
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to one end of C1
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to pins 14 and 13 of U1
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- pin 8 of the joystick connector to the other end of C1
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to pins 2, 4, 5, 7, 9, and 10 of U1
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- pin 15 of the joystick connector to pin 1 of U1
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- pin 4 of the joystick connector to pin 11 of U1
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- pin 12 of U1 to pin 3 of U1
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to the other end of R1
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to the data I/O pins of your 1-Wire devices
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The 1-Wire bus is held high by R1. Devices pull the bus low to send a
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signal; the length of time they hold the bus low determines the type of
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signal. When AN0 is off, the output of U1A is in a high-impedance state so
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that 1-Wire devices can be read through U1B (wired as a buffer) on PB2.
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When AN0 is on, the output of U1A is driven low to send a signal to the bus.
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C1 is a bypass capacitor across the power-input pins of U1. Since U1 is a
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CMOS device, the unused inputs of U1C and U1D are held low.
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Timing diagrams for the different signals used on the 1-Wire bus are in
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Maxim application note #126 (available at
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http://www.maxim-ic.com/appnotes.cfm/appnote_number/522/ln/en).
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At the time I wrote this, I was still waiting for a parts shipment to arrive
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from DigiKey. I substituted a 74F00 and 74F125 from the junkbox, and the
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circuit worked OK I suspect other logic types with TTL-compatible I/O would
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also work. Use 1/4 of the 74F00 as an inverter between AN0 and pin 1 of the
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74F125, since the outputs of the '125 are active when the control input is
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low (on the '126, the outputs are active when the control input is high).
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This circuit doesn't provide parasitic power to 1-Wire devices, so make sure
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their power and ground pins are connected to suitable supplies. Parasitic
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power is described in the datasheets of those devices that support it;
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modifying this interface to support it is left as an exercise for the
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reader.
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