DocID13284 Rev 2
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UM0404
Parallel ports
When using these alternate functions, the user must set the direction of the port line to
output (DP3.y = 1) and must set the port output latch (P3.y = 1). Otherwise the pin is in its
high-impedance state (when configured as input) or the pin is stuck at '0' (when the port
output latch is cleared). When the alternate output functions are not used, the “Alternate
Data Output” line is in its inactive state, which is a high level ('1'). Port3 pins with alternate
output functions are: T6OUT, T3OUT, TxD0, BHE and CLKOUT.
When the on-chip peripheral associated with a Port3 pin is configured to use both the
alternate input and output function, the descriptions above apply to the respective current
operating mode. The direction must be set accordingly. Port3 pins with alternate
input/output functions are: MTSR0, MRST0, RxD0 and SCLK0.
Note:
Enabling the CLKOUT function automatically enables the P3.15 output driver. Setting bit
DP3.15 = ’1’ is not required.
Figure 36. Block diagram of a Port3 pin
Pin P3.12 (BHE/WRH) is another pin with an alternate output function; however, its structure
is slightly different (see
). 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
Open Drain
Latch
Write ODP3.y
Read ODP3.y
Direction
Latch
Write DP3.y
Read DP3.y
In
te
rn
a
l B
u
s
MUX
0
1
Alternate Data Input
Input
Latch
Clock
P3.y
Output
Buffer
y = 13, 11...0
Port Output
Latch
Read P3.y
Write P3.y
&
Alternate
Data Input
Port Data
Output