NXP Semiconductors MC9S08LG16, Reference Manual

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Chapter 2 Pins and Connections
MC9S08LG32 MCU Series, Rev. 5
36 Freescale Semiconductor
depending on the VSUPPLY bits. When V
LL3
is connected to V
DD
externally, VSUPPLY = 11,
FCDEN = 1, and RVEN = 0, the pins operate as full complementary drive. For all other VSUPPLY modes,
the LCD/GPIO operates as open drain.
NOTE
For GPIO muxed with LCD pins, full complimentary or open drain drive is
controlled by the LCD controller. When LCD pins are configured as open
drain GPIOs, then the internal pullup is not disabled in output mode and is
controlled by the GPIO pull control register. This can cause some leakage
from the pads if a pullup is enabled and a zero is being driven.
2.3.7 General-Purpose I/O (GPIO) and Peripheral Ports
The MC9S08LG32 series of MCUs support up to 69 GPIO pins including 2 output-only pins that are
shared with on-chip peripheral functions (timers, serial I/O, LCD, ADC, etc.). The GPIO output-only pins
(PTC5/BKGD/MS and PTC6/RESET) are bi-directional when configured as BKGD and RESET,
respectively.
GPIO that is muxed with LCD pins can be configured to reference V
DD
or V
LL3
. See Section 2.3.6.2,
“LCD Driver Pins ,” for more details.
When a port pin is configured as a general-purpose output or a peripheral uses the port pin as an output,
the software can select one of the two drive strengths and can enable or disable the slew rate control. When
a port pin is configured as a general-purpose input or a peripheral uses the port pin as an input, the software
can enable a pullup device.
When an on-chip peripheral system is controlling a pin, the data direction control bits still determine what
is read from port data registers even though the peripheral module controls the pin direction by controlling
an enable for the pin’s output buffer. For information about controlling these pins as general-purpose I/O
pins, see
Chapter 6, “Parallel Input/Output Control .”
NOTE
• To avoid extra current drain from floating input pins, the reset
initialization routine in the application program must either enable
on-chip pullup devices or change the direction of unused or non-bonded
pins to outputs so they do not float.
• When using RESET pin as bi-directional reset and LCD pins as
open-drain GPIO, the internal pullups are not disabled when these pins
are used in output mode. This can cause some current leakage through
the pads if zero is driven. This is also true for stop2 mode.
Table 2-1. Pin Availability by Package Pin-Count
Packages <-- Lowest Priority --> Highest
80 64 48 Port Pin Alt 1 Alt 2 Alt 3 Alt 4
1 1 1 PTD7 LCD7 — — —
2 2 2 PTD6 LCD6 — — —