4. FDC Description (82078)
21
Tape Drive Register (TDR)
3F3h Default
This register allows you to assign tape support to a particular drive during initialization.
Any future reference to that drive number automatically invokes tape support. This
register is cleared by a hardware reset; software resets have no effect. Bits 2-7 are part
of the "enhanced" tape drive register and are made available only when the EREG EN
bit is set; otherwise, the bits are not driven.
7
6
5
4
3
2
1
0
MEDID1
MEDID0
DRVID1
DRVID0
BOOTSEL1
TAPESEL0
TAPESEL1
BOOTSEL0
Tape Drive Register
Bits 2 through 7 are not writable and remain three-stated if read when EREG EN is not
set. Bits 4 through 7 are not writable, but return the states of the DRVID0, DRVID1,
MEDID0, and MEDID1 pins when EREG EN is set. The EREG EN bit is part of the
COMMAND SET and can be found in the 82078 data sheet.
Bits 0 and 1, the TAPESEL0 and TAPESEL1 bits, allow you to select which drive is to
be configured for tape drive support, as shown in the "
Tape Drive Register Selection
"
table. The Tape Select bits are hardware RESET to 0, making Drive 0 not available for
tape support. Drive 0 is reserved for the floppy boot drive on reset.
Bits 2 and 3, the BOOTSEL0 and BOOTSEL1 bits, are not reset by software resets
and are decoded as shown in the "
Boot Drive Selection Options
" table. These bits allow
for reconfiguring the boot-up drive and are reset only by a hardware reset. A drive can
be enabled by remapping the internal DS0 and ME0 nodes to one of the other drive
select and motor enable lines. Once a non-default value for BOOTSEL1 and
BOOTSEL0 is selected, all programmable bits are virtual designations of drives; it is the
user's responsibility to know the mapping scheme in the following table.
Tape Drive Register Selection
TAPESEL1
TAPESEL0
Drive Selected
0
0
None
0
1
1
1
0
2
1
1
3
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