Normal Floppy Mode
Normal mode. Register 3F3 contains only bits 0 and 1. When this register is read, bits 2 - 7 are a
high impedance.
DB7
DB6
DB5
DB4
DB3
DB2
DB1
DB0
REG 3F3 Tri-state Tri-state Tri-state Tri-state Tri-state Tri-state tape sel1 tape sel0
Enhanced Floppy Mode 2 (OS2)
Register 3F3 for Enhanced Floppy Mode 2 operation.
DB7
DB6
DB5
DB4
DB3
DB2
DB1
DB0
REG 3F3 Reserved Reserved
Drive Type ID
Floppy Boot Drive tape sel1 tape sel0
For this mode, DRATE0 and DRATE1 pins are
inputs, and these inputs are gated into bits 6
and 7 of the 3F3 register. These two bits are
not affected by a hard or soft reset.
Which two bits depends on the last drive
selected in the Digital Output Register (3F2).
(See Table 11)
BITS 3 and 2 Floppy Boot Drive - These bits
reflect the value of configuration register 7 bits
1, 0. Bit 3 = CR7 Bit DB1. Bit 2 = CR7 Bit DB0.
BIT 7 Reserved
BIT 6 Reserved
Bits
1
and
0
-
Tape Drive Select
BITS 5 and 4 Drive Type ID - These Bits reflect
two of the bits of configuration register 6.
(READ/WRITE). Same as in Normal and
Enhanced Floppy Mode. 1.
Table 9 - Drive Type ID
Digital Output Register
Register 3F3 - Drive Type ID
Bit 1
Bit 0
Bit 5
Bit 4
0
0
1
1
0
1
0
1
CR6 - Bit 1
CR6 - Bit 3
CR6 - Bit 5
CR6 - Bit 7
CR6 - Bit 0
CR6 - Bit 2
CR6 - Bit 4
CR6 - Bit 6
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