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1986-01-15
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4KB
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101 lines
External Disk Interface Connector Specification
------------------------------------------------------------
The 23 pin D type connector with sockets (DB23S) at the
rear of the Amiga is nominally used to interface to MFM
devices.
External Disk Connector Pin Assignment (J7)
pin name dir notes
--------------------------
1 RDY* I/O If motor on, indicates disk installed and up to
speed. If motor not on, Identification mode.
(See below.)
2 DKRD* I MFM input data to Amiga
3 GND
4 GND
5 GND
6 GND
7 GND
8 MTRXD* OC Motor on data, clocked into drive's motor on
flip flop by the active transition of SELxB*.
Guaranteed setup time is 1.4 usec. Guaranteed
hold time is 1.4 usec.
9 SEL2B* OC Select drive 2
10 DRESB* OC Amiga system reset. Drives should reset their
motor on flip flops and set their write
protect flip flops.
11 CHNG* I/O Note: Nominally used as an open collector input.
Drive's change flop is set at power up or when
no disk is not installed. Flop is reset when
drive is selected and the head stepped, but
only if a disk is installed.
12 +5V 270 ma maximum; 410 ma surge. When below 3.75V,
drives are required to reset their motor on
flops, and set their write protect flops.
13 SIDEB* O Side 1 if active, side 0 if inactive
14 WPRO* I/O Asserted by selected, write protected disk.
15 TK0* I/O Asserted by selected drive when read write head
is positioned over track 0.
16 DKWEB* OC Write gate (enable) to drive.
17 DKWDB* OC MFM output data from Amiga.
18 STEPB* OC Selected drive steps one cylinder in the
direction indicated by DIRB.
19 DIRB OC Direction to step the head. Inactive to step
towards center of disk (higher numbered
tracks).
20 SEL3B* OC Select drive 3.
21 SEL1B* OC Select drive 1.
22 INDEX* I/O Index is a pulse generated once per disk
revolution between the end and beginning of
cylinders. The 8520 can be programmed to
conditionally generate a level 6 interrupt
to the 68000 whenever the INDEX* input goes
active.
23 +12V 160 ma maximum; 540 ma surge
External Disk Connector Identification Mode
--------------------------------------------------
An identification mode is provided for reading a 32 bit serial
identification data stream from an external device. To initialize
this mode, the motor must be turned on then off. See pin 8,
MTRXD* for a discussion of how to turn the motor on and off. The
transition from motor on to motor off reinitializes the serial
shift register. After initialization, the SELxB* signal should be
left in the inactive state. Now enter a loop where SELxB* is driven
active, read serial input data on RDY* (pin 1), and drive SELxB*
inactive. Repeat this loop a total of 32 times to read in 32 bits
of data. The most significant bit is received first.
External Disk Connector Defined Identifications
--------------------------------------------------
$0000 0000 - no drive present
$FFFF FFFF - Amiga standard 3.25 diskette
$5555 5555 - 48 TPI double density double sided
As with other peripheral ID's, users should contact Commodore-Amiga
(mailbox: amiga) for ID assignment. The serial input data is
active low and must therefore be inverted to be consistant with the
above table.
External Disk Connector Limitations
--------------------------------------------------
1. The total cable length including daisy chaining must
not exceed 1 meter.
2. A maximum of 3 external devices may reside on this interface.
3. Each device must provide a 1000 Ohm pull up resistor on those
outputs driven by an open collector device on the Amiga
(pins 8-10, 16-21).