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 (READ/WRITE). Same
as in Normal and Enhanced Floppy Mode. 1.
BITS 5 and 4 Drive Type ID - These Bits reflect two of
the bits of configuration register 6.
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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