Toshiba TLCS-900/H1 Series Manual page 126

(3) The cautions at the time of the functional change of a
A chip select signal output has the case of a combination terminal with a general-purpose
port function. In this case, an output latch register and a function control register are
initialized by the reset action, and an object terminal is initialized by the port output ("1" or
"0") by it.
Functional change
Although an object terminal is changed from a port to a chip select signal output by
setting up a function control register (PnFC register), the short pulse for several ns
may be outputted to the changing timing. Although it does not become especially a
problem when using the usual memory, it may become a problem when using a special
memory.
* XX is a function register address.(When an output port is initialized by "0")
Internal address bus
Function control signal
Pxx
A23 to A0
The measure by software
The countermeasures in S/W for avoiding this phenomenon are explained.
Since CS signal decodes the address of the access area and is generated, an
unnecessary pulse is outputted by access to the object CS area immediately after
setting it as a CSn function. Then, if internal area is accessed also immediately after
setting a port as CS function, an unnecessary pulse will not output.
1. The ban on interruption under functional change (DI command)
2. A dummy command is added in order to carry out continuous internal access.
3. (Access to a functional change register is corresponded by 16-bit command.
(LDW command))
Internal address bus
Function control signal
Pxx
A23 to A0
A port is set as CSn .
n
XX
Output port
n
A port is set as .
CSn
XX XX+1
Output port
CSn
n
92CH21-124
.
CSn
n+2
CSn
n+2
Output pulse
t
AD3
Dummy access
n+2
n+2
TMP92CH21
2009-06-19