Datasheet

Chapter 6 Parallel Input/Output
MC9S08AC16 Series Data Sheet, Rev. 9
92 Freescale Semiconductor
6.7.3 Port B I/O Registers (PTBD and PTBDD)
Port B parallel I/O function is controlled by the registers in this section.
76543210
R
R R R R PTBD3 PTBD2 PTBD1 PTBD0
W
Reset00000000
Figure 6-15. Port B Data Register (PTBD)
1
1
Bits 7 through 4 are reserved bits that must always be written to 0.
Table 6-6. PTBD Register Field Descriptions
Field Description
3:0
PTBD[3:0]
Port B Data Register Bits — For port B pins that are inputs, reads return the logic level on the pin. For port B
pins that are configured as outputs, reads return the last value written to this register.
Writes are latched into all bits of this register. For port B pins that are configured as outputs, the logic level is
driven out the corresponding MCU pin.
Reset forces PTBD to all 0s, but these 0s are not driven out the corresponding pins because reset also configures
all port pins as high-impedance inputs with pullups disabled.
76543210
R
R R R R PTBDD3 PTBDD2 PTBDD1 PTBDD0
W
Reset00000000
Figure 6-16. Data Direction for Port B (PTBDD)
1
1
Bits 7 through 4 are reserved bits that must always be written to 0.
Table 6-7. PTBDD Register Field Descriptions
Field Description
3:0
PTBDD[3:0]
Data Direction for Port B Bits — These read/write bits control the direction of port B pins and what is read for
PTBD reads.
0 Input (output driver disabled) and reads return the pin value.
1 Output driver enabled for port B bit n and PTBD reads return the contents of PTBDn.