ZX-Spectrum +3's Auxiliary interface

The AUX (auxiliary interface) socket supports two input lines (pins 2 and 5) and two output lines (pins 2 and 4). The I/O lines are driven by 1488 and 1489 line driver chips which are, in turn, connected to the I/O lines of the AY-3-8912 (see the manufacturer's data sheet for this device). Basically, register 16 of the AY-3-8912 controls eight I/O lines, the bits are designated as follows...

BIT	SIGNAL
0	AUX pin 2 (out)
1	AUX pin 4 (out)
2	RS232 pin 5 (CTS out)
3	RS232 pin 3 (RXD out)
4	AUX pin 3 (in)
5	AUX pin 5 (in)
6	RS232 pin 4 (DTR in)
7	RS232 pin 5 (TXD in)

Using software control loops, the I/O lines could be driven as a second RS232 port (in the same way as the RS232/MIDI socket is driven using bits 2, 3, 6 and 7). Alternatively, the I/O lines could be used to drive, for example, a robot or some other external device.

     ___________________________
  __|   6   5   4   3   2   1   |
 |__   ### ### ### ### ### ###  |
    |___________________________|

             AUX socket

PIN	FUNCTION
1	GND
2	OUTPUT BIT 0
3	INPUT BIT 4
4	OUTPUT BIT 1
5	INPUT BIT 5
6	+12V

Source: [The Hardware Book]

[Back]