The Amiga can read and interpret many different and nonstandard controllers. The control lines built into the POTGO register (address $DFF034) can redefine the functions of some of the controller port pins. Table 8-4 is the POTGO register bit description. POTGO ($DFF034) is the write-only address for the pot control register. POTGOR (formerly POTINP) ($DFF016) is the read-only address for the pot control register. The pot-control register controls a four-bit bidirectional I/O port that shares the same four pins as the four pot inputs. Table 8-4: POTGO ($DFF034) and POTGOR ($DFF016) Registers Bit Number Name Function ------ ---- -------- 15 OUTRY Output enable for bit 14 (1=output) 14 DATRY data for port 2, pin 9 13 OUTRX Output enable for bit 12 12 DATRX data for port 2, pin 5 11 OUTLY Output enable for bit 10 10 DATLY data for port 1, pin 9 (right mouse button ) 09 OUTLX Output enable for bit 8 08 DATLX data for port 1, pin 5 (middle mouse button ) 07-01 X chip revision identification number 00 START Start pots (dump capacitors, start counters) Instead of using the pot pins as variable-resistive inputs, you can use these pins as a four-bit input/output port. This provides you with two additional pins on each of the two controller ports for general purpose I/O. If you set the output enable for any pin to a 1, the Amiga disconnects the potentiometer control circuitry from the port, and configures the pin for output. The state of the data bit controls the logic level on the output pin. This register must be written to at the POTGO address, and read from the POTGOR address. There are large capacitors on these lines, and it can take up to 300 microseconds for the line to change state. To use the entire register as an input, sensing the current state of the pot pins, write all 0s to POTGO. Thereafter you can read the current state by using read-only address POTGOR. Note that bits set as inputs will be connected to the proportional counters (See the description of the START bit in POTGO). These lines can also be used for button inputs. A button is a normally open switch that shorts to ground. The Amiga must provide a pull-up resistance on the sense pin. To do this, set the proper pin to output, and drive the line high (set both OUT... and DAT... to 1). Reading POTGOR will produce a 0 if the button is pressed, a 1 if it is not. The joystick fire buttons can also be configured as outputs. CIAADDRA ($BFE201) contains a mask that corresponds one-to-one with the data read register, CIAAPRA ($BFE001). Setting a 1 in the direction position makes the corresponding bit an output. See Appendix F for more details.
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