TAPE DRIVE REGISTER (TDR)
Address 3F3 READ/WRITE
TABLE 7 - TAPE SELECT BITS
TAPE SEL1
(TDR.1)
TAPE SEL0
(TDR.0)
DRIVE
SELECTED
0
0
1
1
0
1
0
1
None
1
2
3
The
Tape
Drive
TABLE 7 illustrates the
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.
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.
TABLE 8 - INTERNAL 2 DRIVE DECODE - NORMAL
DRIVE SELECT OUTPUTS
(ACTIVE LOW)
nDS1 nDS0
MOTOR ON OUTPUTS
(ACTIVE LOW)
DIGITAL OUTPUT REGISTER
Bit 7 Bit 6 Bit 5 Bit 4 Bit1 Bit 0
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
0
X
1
X
X
0
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
0
TABLE 9 - 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
0
X
1
X
X
0
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
0
21
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