sc9s08mz16 Freescale Semiconductor, Inc, sc9s08mz16 Datasheet - Page 28

• Manufacturer Part Number: sc9s08mz16
• Description: Hcs08 Microcontrollers
• Manufacturer: Freescale Semiconductor, Inc

Chapter 2 Pins and Connections
external reset circuitry unnecessary. This pin is normally connected to the standard 6-pin background
debug connector so a development system can directly reset the MCU system. If desired, a manual external
reset can be added by supplying a simple switch to ground (pull reset pin low to force a reset).
Whenever any reset is initiated (whether from an external signal or from an internal system), the reset pin
is driven low for approximately 34 bus cycles. The reset circuitry decodes the cause of reset and records
it by setting a corresponding bit in the system control reset status register (SRS).
In EMC-sensitive applications, an external RC filter is recommended on the reset pin. See
an example.
2.3.4
While in reset, the BKGD/MS pin functions as a mode select pin. Immediately after reset rises the pin
functions as the background pin and can be used for background debug communication. While functioning
as a background/mode select pin, the pin includes an internal pullup device, input hysteresis, a standard
output driver, and no output slew rate control.
If nothing is connected to this pin, the MCU will enter normal operating mode at the rising edge of reset.
If a debug system is connected to the 6-pin standard background debug header, it can hold BKGD/MS low
during the rising edge of reset which forces 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 bus clock rate, so there should 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.
2.3.5
The V
for the ADC module.
2.3.6
The IRQ pin is the input source for the IRQ interrupt and is also the input for the BIH and BIL instructions.
If the IRQ function is not enabled, this pin does not perform any function.
In EMC-sensitive applications, an external RC filter is recommended on the IRQ pin. See
an example.
28
REFH
Background/Mode Select (BKGD/MS)
ADC Reference Pins (V
and V
External Interrupt Pin (IRQ)
REFL
pins are the voltage reference high and voltage reference low inputs respectively
SC9S08MZ16 MCU Data Sheet, Rev. 0 Draft C
REFH
, V
REFL
)
Freescale Semiconductor
Figure 2-3
Figure 2-3
for
for