MC9S08QG8 Datasheet, PDF (83/300 Pages) Freescale Semiconductor, Inc – 8-BIT HCS08 Central Processor Unit

Chapter 6 Parallel Input/Output Control
6.4.4.3 Port B Drive Strength Select (PTBDS)
An output pin can be selected to have high output drive strength by setting the corresponding bit in the
drive strength select register (PTBDSn). When high drive is selected a pin is capable of sourcing and
sinking greater current. Even though every I/O pin can be selected as high drive, the user must ensure that
the total current source and sink limits for the chip are not exceeded. Drive strength selection is intended
to affect the DC behavior of I/O pins. However, the AC behavior is also affected. High drive allows a pin
to drive a greater load with the same switching speed as a low drive enabled pin into a smaller load.
Because of this the EMC emissions may be affected by enabling pins as high drive.
R
W
Reset:
7
PTBDS7
0
6
PTBDS6
5
PTBDS5
4
PTBDS4
3
PTBDS3
2
PTBDS2
1
PTBDS1
0
0
0
0
0
0
Figure 6-16. Drive Strength Selection for Port B Register (PTBDS)
Table 6-10. PTBDS Register Field Descriptions
0
PTBDS0
0
Field
Description
7:0
PTBDS[7:0]
Output Drive Strength Selection for Port B Bits — Each of these control bits selects between low and high
output drive for the associated PTB pin. For port B pins that are configured as inputs, these bits have no effect.
0 Low output drive strength selected for port B bit n.
1 High output drive strength selected for port B bit n.
MC9S08QG8 and MC9S08QG4 Data Sheet, Rev. 1.01
Freescale Semiconductor
83