appear on SD0-7. If nROMCS = 1, the RD bus is
disabled, and nothing appears on the SD bus.
Note: any RD bus pin can be programmed as an
alternate function, however, if nROMCS=0, then
anything on the RD bus will appear on the SD bus.
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
Case 3: nROMCS as GPIO function. (nROMCS
internally tied to VDD.) The RD bus
alternate function.
These alternate functions
floats - cannot use as a bus. Any pin can be
programmed as an alternate function.
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 4: nROMCS and nROMOE as GPIO
function. Same as Case 3.
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
Case 5: Parallel IRQ enabled; RD Bus pins,
nROMOE, nROMCS are used as IRQ pins.
107
SMSC [ SMSC CORPORATION ]
