Datasheet

ST10F269 12 - PARALLEL PORTS
75/184
Pin P3.12 (BHE/WRH) is another pin with an
alternate output function, however, its structure is
slightly different.
After reset the BHE
or WRH function must be
used depending on the system start-up
configuration. In either of these cases, there is no
possibility to program any port latches before.
Thus, the appropriate alternate function is
selected automatically. If BHE
/WRH is not used in
the system, this pin can be used for general
purpose I/O by disabling the alternate function
(BYTDIS = ‘1’ / WRCFG=’0’).
Note: Enabling the BHE
or WRH function automatically enables the P3.12 output driver. Setting bit
DP3.12=’1’ is not required.
During bus hold pin P3.12 is switched back to its standard function and is then controlled by
DP3.12 and P3.12. Keep DP3.12 = ’0’ in this case to ensure floating in hold mode.
Figure 29 : Block Diagram of Pins P3.15 (CLKOUT) and P3.12 (BHE
/WRH)
Direction
Latch
Write DP3.x
Read DP3.x
Port Output
Latch
Write P3.x
Read P3.x
Internal Bus
MUX
0
1
MUX
0
1
Alternate
Data
Output
MUX
0
1
“1”
Input
Latch
Clock
P3.12/BHE
P3.15/CLKOUT
Output
Buffer
x = 15, 12
Alternate
Function
Enable