
SMSC DS – FDC37N958FR
Page 126
Rev. 09/01/99
Parallel Port FDC Control
There are two modes of operation, PPFD1 and
PPFD2. These modes can be selected in Global
Configuration Register 0x25 (Device Mode), bits
3 and 4. PPFD1 mode has only drive 1 on the
PPFD1:
Drive 0 is on the FDC pins.
Drive 1 is on the parallel port pins.
Drive 1 is on the FDC pins.
Drive 0 is on the parallel port pins.
PPFD2:
Drive 0 is on the parallel port pins.
Drive 1 is on the parallel port pins.
The following FDC output pins are Open Drain 24mA outputs when the Parallel Port FDC is selected by
the drive select register. Reminder, it is up to the designer to provide pull-up resistors on these FDC
output pins.
nWDATA, DRVDEN0, nHDSELm nWGATE, nDIR, nSTEP, nDS1, nDS0, nMTR0, nMTR1.
Parallel Port - 8051 Control (FDC37N958FR
Standard)
In this mode, the parallel port pins are controlled
by the 8051 through a set of three on-chip
memory mapped registers. The memory mapped
Table 53 - FDC on Parallel Port Activation Control
FDC PARALLEL
PORT MODE
CR25 BITS [4:3]
L0-CR30-BIT0
DOWN
ACTIVE BIT
01 or 10
0
x
01 or 10
1
N
01 or 10
1
Y
00 or 11
x
x
00 or 11
x
x
00 or 11
x
x
00 or 11
x
x
Inactive = Hi-z on pins
Active = OD24/O24 as per selected mode.
The FDD pins that are multiplexed onto the Parallel Port function independently of the state of the
Parallel Port logical device. This affects the pins when CR25 bits [4:3] are 01 or 10.
(Note: FDC Mode Bits L0-CRF0-B[7:6] have no effect on the parallel port Pins).
parallel port pins; PPFD2 mode has drive 0 and
1 on the parallel port pins. Note: The Drive
Swap bit, FDD Mode Configuration Register bit-4
(LD0_CRF0), can be used to swap the motor
and drive select outputs on of the Parallel Port
FDC.
Drive Swap bit = 0
Drive Swap bit = 1
registers are the PAR PORT STATUS, the PAR
PORT CONTROL, and the PAR PORT DATA
registers. In this mode, the parallel port pins are
not controlled by the parallel port logical device.
Refer to the 8051 section of this specification for
information on these control registers.
FDC ACTIVE BIT
FDC IN
POWER
PARALLEL
PORT
PARALLEL
PORT IN
POWER
DOWN
x
x
x
x
N
Y
x
PP_
HA
1
1
1
1
1
1
0
PARALLEL PORT
PINS
(MODE) STATE
(FDC) Inactive
(FDC) Active
(FDC) Inactive
(Parallel Port) Inactive
(Parallel Port) Active
(Parallel Port) Inactive
(8051 Mode) Active
x
x
x
0
1
1
x