
MC68HC16R1/916R1
USER’S MANUAL
REGISTER SUMMARY
MOTOROLA
D-11
D.2.9 Port E Data Register
This register can be accessed in two locations and can be read or written at any time.
A write to this register is stored in an internal data latch, and if any pin in the
corresponding port is configured as an output, the value stored for that bit is driven out
on the pin. A read of this data register returns the value at the pin only if the pin is
configured as a discrete input. Otherwise, the value read is the value stored in the
register. Bits [15:8] are unimplemented and will always read zero.
D.2.10 Port E Data Direction Register
The port E data direction register controls the direction of the port E pin drivers when
pins are configured for I/O. Setting a bit configures the corresponding pin as an output;
clearing a bit configures the corresponding pin as an input. This register can be read
or written at any time.
The port A/B data direction register controls the direction of the pin drivers for ports A
and B, respectively, when the pins are configured for I/O. Setting DDA or DDB to one
configures all pins in the corresponding port as outputs. Clearing DDA or DDB to zero
configures all pins in the corresponding port as inputs. Bits [15:10] are unimplemented
and will always read zero.
D.2.11 Port E Pin Assignment Register
This register determines the function of port E pins. Setting a bit assigns the corre-
sponding pin to a bus control signal; clearing a bit assigns the pin to I/O port E. PE3 is
not connected to a pin. PEPA3 can be read and written, but has no function. Bits [15:8]
are unimplemented and will always read zero.
Table D-4
displays port E pin
assignments.
PORTE0
—
Port E0 Data Register
PORTE1
—
Port E1 Data Register
$YFFA10
$YFFA12
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0
NOT USED
PE7
PE6
PE5
PE4
PE3
PE2
PE1
PE0
RESET:
U
U
U
U
U
U
U
U
DDRAB
— Port A/B Data Direction Register
DDRE —
Port E Data Direction Register
$YFFA14
$YFFA15
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0
0
0
0
0
0
0
DDA
DDB
DDE7
DDE6
DDE5
DDE4
DDE3
DDE2
DDE1
DDE0
RESET:
0
0
0
0
0
0
0
0
PEPAR —
Port E Pin Assignment
$YFFA17
15
8
7
6
5
4
3
2
1
0
NOT USED
PEPA7
PEPA6
PEPA5
PEPA4
PEPA3
PEPA2
PEPA1
PEPA0
RESET:
DATA8
DATA8
DATA8
DATA8
DATA8
DATA8
DATA8
DATA8