
82091AA
APPENDIX A
FDC FOUR DRIVE SUPPORT
Section 8.0 of this document completely describes the FDC when the module is configured for two drive
support. In addition, the FDC commands in Section 8.0 provide four drive support information. This appendix
provides additional information concerning four drive support. The signal pins that are affected by four drive
support are described in Section A.1. Note that the FDC signals not discussed in this appendix operate the
same for both two and four drive systems. The following registers are described in this appendix; Digital Output
Register (DOR), Enhanced Tape Drive Register (TDR), and the Main Status Register (MSR). Some bits in
these registers operate differently in a four drive configuration than a two drive configuration.
NOTES:
#
The descriptions in this appendix assume that four floppy drive support has been selected by setting
FDDQTY to 1 in the AIPCFG1 Register.
#
Only drive 0 or drive 1 can be selected as the boot drive.
A.1 Floppy Disk Controller Interface Signals
These signal descriptions are for a four drive system (FDDQTY
e
1 in the AIPCFG1 Register). See Section 2.0
for two drive system signal descriptions.
Signal Name
Type
Description
FDME1
Y
/DSEN
Y
(1)
O
FLOPPY DRIVE MOTOR ENABLE 1, or DRIVE SELECT ENABLE:
In a
four drive system, this signal functions as a drive select enable
(DSEN
Y
). When DSEN
Y
is asserted, MDS1 and MDS0 reflect the
selection of the drive.
FDS1
Y
/MDS1
(1)
O
FLOPPY DRIVE SELECT1, or MOTOR DRIVE SELECT 1:
In a four
drive system, this signal functions as a motor drive select (MDS1).
MDS1, together with MDS0, indicate which of the four drives is selected,
as shown in note 1.
FDME0
Y
/MEEN
Y
(1)
O
FLOPPY DRIVE MOTOR ENABLE 0 or MOTOR ENABLE ENABLE:
In
a four drive system, this signal functions as a motor enable enable
(MEEN
Y
). MEEN
Y
is asserted to enable the external decoding of MDS1
and MDS0 for the appropriate motor enable (see note 1).
FDS0
Y
/MDS0
(1)
O
FLOPPY DRIVE SELECT 0 or MOTOR DRIVE SELECT 0:
In a four
drive system, this signal functions as motor drive select (MDS0). MDS0,
together with MDS1, indicate which of the four drives is selected as
shown in note 1.
NOTE:
1. These signal pins are used to control an external decoder for four floppy disk drives as shown below. Refer to the DOR
Register Description in Section A.2 for details.
DSEN
Y
e
0
MEEN
Y
e
0
0
0
Drive 0
ME0
0
1
Drive 1
ME1
1
0
Drive 2
ME2
1
1
Drive 3
ME3
MDS1
MDS0
A-1