mc9s08sg4 Freescale Semiconductor, Inc, mc9s08sg4 Datasheet - Page 27
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mc9s08sg4
Manufacturer Part Number
mc9s08sg4
Description
8-bit Microcontroller Family
Manufacturer
Freescale Semiconductor, Inc
Datasheet
1.MC9S08SG4.pdf
(320 pages)
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2.2.4
During a power-on-reset (POR) or background debug force reset (see
Debug Force Reset Register
select pin. Immediately after any reset, the pin functions as the background pin and can be used for
background debug communication. The BKGD/MS pin contains an internal pullup device.
If nothing is connected to this pin, the MCU will enter normal operating mode at the rising edge of the
internal reset after a POR or force BDC reset. If a debug system is connected to the 6-pin standard
background debug header, it can hold BKGD/MS low during a POR or immediately after issuing a
background debug force reset, which will force the MCU to active background mode.
The BKGD pin is used primarily for background debug controller (BDC) communications using a custom
protocol that uses 16 clock cycles of the target MCU’s BDC clock per bit time. The target MCU’s BDC
clock could be as fast as the maximum bus clock rate, so there must never be any significant capacitance
connected to the BKGD/MS pin that could interfere with background serial communications.
Although the BKGD pin is a pseudo open-drain pin, the background debug communication protocol
provides brief, actively driven, high speedup pulses to ensure fast rise times. Small capacitances from
cables and the absolute value of the internal pullup device play almost no role in determining rise and fall
times on the BKGD pin.
2.2.5
The MC9S08SG8 series of MCUs support up to 16 general-purpose I/O pins which are shared with
on-chip peripheral functions (timers, serial I/O, ADC, etc.).
When a port pin is configured as a general-purpose output or a peripheral uses the port pin as an output,
software can select one of two drive strengths and enable or disable slew rate control. When a port pin is
configured as a general-purpose input or a peripheral uses the port pin as an input, software can enable a
pull-up device. Immediately after reset, all of these pins are configured as high-impedance general-purpose
inputs with internal pull-up devices disabled.
When an on-chip peripheral system is controlling a pin, data direction control bits still determine what is
read from port data registers even though the peripheral module controls the pin direction by controlling
the enable for the pin’s output buffer. For information about controlling these pins as general-purpose I/O
pins, see
Freescale Semiconductor
Chapter 6, “Parallel Input/Output
Background / Mode Select (BKGD/MS)
General-Purpose I/O and Peripheral Ports
The voltage measured on the internally pulled up RESET pin will not be
pulled to V
the RESET pin is required to drive to a V
be used.
In EMC-sensitive applications, an external RC filter is recommended on the
RESET. See
DD
Figure 2-4
(SBDFR),” for more information), the BKGD/MS pin functions as a mode
. The internal gates connected to this pin are pulled to V
MC9S08SG8 MCU Series Data Sheet, Rev. 3
for an example.
Control.”
NOTE
DD
level an external pullup should
Section 5.7.2, “System Background
Chapter 2 Pins and Connections
DD
. If
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