Commodore Amiga A500 Technical Reference Manual page 9

External Disk Interface
Connector
The 23 pin D-type connector with sockets (DB23S) at the rear of the
Amiga is nominally used to interface to MFM devices.
The second disk drive port is similar to the A1000, and is therefore
compatible with the 1010 or the 1020 disk drive. The CPU will
power one external 1010 disk drive.
External Disk Connector Pin Assignment
Pin Name
1 RDY*
2 DKRD*
3 GND
4 GND
5 GND
6 GND
7 GND
8 MTRXD*
9 SEL2B*/SEL3B
*
10 DRESB*
11 CHNG*
12 5V
13 SIDEB*
14 WPR0*
6
Dir Notes
I/O If motor on, indicates disk
installed and up to speed.
If motor not on, Identification
mode. See below.
I MFM input data to Amiga.
OC Motor on data, clocked into
drive's motor on flip flops by the
active transistion of SELxB*.
Guaranteed setup time is 1.4
μsec
Guaranteed hold time is 1.4
μsec.
0C A500:Select drive 2/A2000:
Select drive 3.
OC Amiga system reset. Drives
should reset their motor on flip
flops and set their write protect
flip flops.
I/0 Note: Nominally used as an open
collector input. Drive's change
flop is set at power-up or when
no disk is installed. Flop is reset
when drive is selected and the
head stepped, but only if a disk is
installed.
270 ma maximum; 410 ma
surge.
When below 3.75V, drives are
required to reset their motor on
flops, and set their write protect
on flops.
0 Side 1 if active, side 0 if inactive.
I/O Asserted by selected, write
protected disk.