TAPE DRIVE REGISTER (TDR)
Address 3F3 READ/WRITE
Table 4- Tape Select Bits
The Tape Drive Register (TDR) is included for
82077 software compatibility and allows the
user to assign tape support to a particular drive
during initialization. Any future references to
that drive automatically invokes tape support.
The TDR Tape Select bits TDR [1:0] determine
the tape drive number. Table 4 illustrates the
Tape Select bit encoding. Note that drive “0” is
the boot device and cannot be assigned tape
support. The remaining Tape Drive Register
bits TDR.[7:2] are tristated when read. The TDR
is unaffected by a software reset.
TAPE SEL1
TAPE SEL0
(TDR.0)
DRIVE
SELECTED
(TDR.1)
0
0
1
1
0
1
0
1
None
1
2
3
Table 5 - Internal 2 Drive Decode - Normal
DRIVE SELECT
MOTOR ON OUTPUTS
(ACTIVE LOW)
DIGITAL OUTPUT REGISTER
OUTPUTS (ACTIVE LOW)
Bit 7 Bit 6 Bit 5 Bit 4 Bit1 Bit 0
nDS1
nDS0
nMTR1
nBIT 5
nBIT 5
nBIT 5
nBIT 5
nBIT 5
nMTR0
nBIT 4
nBIT 4
nBIT 4
nBIT 4
nBIT 4
X
X
X
1
X
X
1
X
1
1
X
X
X
0
0
0
1
1
X
0
1
0
1
X
1
0
1
1
1
0
1
1
1
1
X
X
0
X
0
0
Table 6 - Internal 2 Drive Decode - Drives 0 and 1 Swapped
DRIVE SELECT
OUTPUTS (ACTIVE
LOW)
MOTOR ON OUTPUTS
(ACTIVE LOW)
DIGITAL OUTPUT REGISTER
Bit 7 Bit 6 Bit 5 Bit 4 Bit1 Bit 0
nDS1
nDS0
nMTR1
nBIT 4
nBIT 4
nBIT 4
nBIT 4
nBIT 4
nMTR0
nBIT 5
nBIT 5
nBIT 5
nBIT 5
nBIT 5
X
X
X
1
X
X
1
X
1
1
X
X
X
0
0
0
1
1
X
0
1
0
1
X
0
1
1
1
1
1
0
1
1
1
X
X
0
X
0
0
18
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