Disk Controller - Commodore Amiga Hardware Reference Manual

Table 8-5: POTGO Register
Bit
Number Name
Function
15
OUTRY Output enable for right port pin 9
14
DATRY I/O data right port pin 9
13 OUTRX
Output enable for right port pin 5
12 DATRX
I/O data right port pin 5
11
OUTLY
Output enable for left port pin 9
10
DATLY I/O data left port pin 9
09 OUTLX Output enable for left port pin 5
08
DATLX I/O data left port pin 5
07-01 X
Reserved for chip identification
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 the equivalent of two additional pins
on each of the two controller ports for general purpose I/O, as shown in table 8-5.
If you set any of the "OUT ... " bits high, it disconnects the potentiometer control circui-
try from the port. The current state of the "DAT ... " pins in this register-lor O-will
appear on the specified port pin. You set the state of the OUT ... and DAT ... pins by
writing into this register through the POTGO address. There are large capacitors on
these lines, and it can take up to 300 microseconds for the line to change state.
To use this register as an input, sensing the current state of the pot pins, write all Os to
POTGO. Thereafter you can read the current state by using read-only address POT-
GOR. Any bits set as inputs will be affected by the START bit of the POTGO register.
You can also use these signals for fire-buttons. To do this, drive the line high (set both
OUT ... and DAT ... to 1). When the button is pressed, the line will be shorted to
ground, and reading POTGOR will produce a O. If the button is not pressed, the read-
ing will be
1.
Disk Controller
The disk controller in this system can handle four double-sided, 3 1/2- or 5 1/4-inch disk
drives. A 3 1/2-inch drive is installed in the basic unit. The other drives are external to
the main box.
Interface Hardware 227