HD64F3437TF16 Datasheet, PDF (157/752 Pages) Hitachi Semiconductor – 12 V must not be applied to the S-mask model (single-power-supply specification), as this may permanently damage the device.

7.6.3 Pin Functions
Port 5 has the same pin functions in each operating mode. All pins can also be used as SCI0
input/output pins. Table 7.11 indicates the pin functions of port 5.
Table 7.11 Port 5 Pin Functions
Pin
P5₂/SCK₀
Pin Functions and Selection Method
Bit C/A in SMR of SCI0, bits CKE0 and CKE1 in SCR of SCI0, and bit P5₂DDR
select the pin function as follows
CKE1
0
1
C/A
0
1
—
CKE0
0
1
—
—
P5₂DDR
Pin function
0
P5₂
input
1
P5₂
output
—
SCK₀
output
—
SCK₀
output
—
SCK₀
input
P5₁/RxD₀
P5₀/TxD₀
Bit RE in SCR of SCI0 and bit P5₁DDR select the pin function as follows
RE
0
1
P5₁DDR
Pin function
0
P5₁ input
1
P5₁ output
—
RxD₀ input
Bit TE in SCR of SCI0 and bit P5₀DDR select the pin function as follows
TE
0
1
P5₀DDR
Pin function
0
P5₀ input
1
P5₀ output
—
TxD₀ output
128