FDC37B78X SMSC Corporation, FDC37B78X Datasheet - Page 122

• Manufacturer Part Number: FDC37B78X
• Description: Enhanced Super I/O Controller with ACPI Support/ Real Time Clock and Consumer IR
• Manufacturer: SMSC Corporation

The chip contains one 245 type buffer that can
be used for a BIOS Buffer. If the BIOS buffer is
not used, then nROMCS must be tied high or
pulled up to Vcc with a resistor so as not to
interfere with the boot ROM.
allows data transmission from the RD bus to the
RD Bus Functionality
The following cases described below illustrate
the use of the RD Bus.
Case 1: nROMCS and nROMOE as original
function. The RD bus can be used as the RD
bus or one or more RD pins can be
programmed as alternate function.
alternate functions behave as follows: if in RD to
SD mode, any value on RDx will appear on SDx;
if in SD to RD mode, SDx will not appear on
RDx, RDx gets the alternate function value.
Note: In this case, nROMCS=0, nROMOE=1.
Case 2: nROMOE as GPIO function. (nROMOE
internally tied to ground). In this case, the RD
bus is a unidirectional bus (read only) controlled
by nROMCS. If nROMCS = 0, the values on
RD0-7 appear on SD0-7. If nROMCS = 1, the
nROMCS
H
L
L
This function
nROMOE
These
BIOS BUFFER
H
X
L
122
SD bus or from the SD bus to the RD bus. The
direction of the transfer is controlled by
nROMOE. The enable input, nROMCS, can be
used to disable the transfer and isolate the
buses.
RD[0:7] data to SD[0:7] bus
SD[0:7] data to RD[0:7]
Isolation
RD bus is disabled, and nothing appears on the
SD bus.
programmed as an alternate function, however,
if nROMCS=0, then anything on the RD bus will
appear on the SD bus.
Case 3: nROMCS as GPIO function. (nROMCS
internally tied to VDD.) The RD bus
floats - cannot use as a bus. Any pin can be
programmed as an alternate function.
Case 4: nROMCS and nROMOE as GPIO
function. Same as Case 3.
Case 5: Parallel IRQ enabled; RD Bus pins,
nROMOE, nROMCS are used as IRQ pins.
DESCRIPTION
Note: any RD bus pin can be