2.2.3 External reset pin (RESET) and interrupt pin (IRQ)
A low on the RESET pin forces the MCU to an known startup state. RESET is
bidirectional, allowing a reset of the entire system. It is driven low when any internal
reset source is asserted. This pin contains an internal pullup resistor.
RESET shares an I/O pin with PTA5. The RESET pin function is enabled by default after
POR reset, because internal power-on reset and low-voltage reset circuitry typically make
external reset circuitry unnecessary. This pin is normally connected to the standard 6-pin
background debug connector so that a development system can directly reset the MCU
system. If RESET function of PTA5/IRQ/FTM1CH0/RESET pin is enabled, a manual
external reset can be added by supplying a simple switch to ground (pull reset pin low to
force a reset). When the RESET pin function is enabled, an internal pullup resistor is
connected to this pin and a reset signal can feed into MCU with an input hysteresis. POR
reset brings RESET pin into its default configuration, reset other than POR has no effect
on the RESET pin function configuration.
When PTA5/IRQ/FTM1CH0/RESET is enabled as IRQ pin, it is the input source for the
IRQ interrupt and is also the input for the BIH and BIL instructions. IRQ is asynchronous
external interrupt pins.
In EMC-sensitive applications, an external RC filter is recommended on the reset pin.
See the following figure for example.
MCU
V
DD
PTA5/IRQ/FTM1CH0/RESET
V
SS
F
0.1
4.7k
10k
Figure 2-6. PTA5/IRQ/FTM1CH0/RESET external RC filter
Pin functions
MC9S08PA4 Reference Manual, Rev. 5, 08/2017
32
NXP Semiconductors
Summary of Contents for MC9S08PA4
Page 1: ...MC9S08PA4 Reference Manual Supports MC9S08PA4 Document Number MC9S08PA4RM Rev 5 08 2017 ...
Page 2: ...MC9S08PA4 Reference Manual Rev 5 08 2017 2 NXP Semiconductors ...
Page 22: ...MC9S08PA4 Reference Manual Rev 5 08 2017 22 NXP Semiconductors ...
Page 28: ...System clock distribution MC9S08PA4 Reference Manual Rev 5 08 2017 28 NXP Semiconductors ...
Page 150: ...Port data registers MC9S08PA4 Reference Manual Rev 5 08 2017 150 NXP Semiconductors ...
Page 196: ...Human machine interfaces HMI MC9S08PA4 Reference Manual Rev 5 08 2017 196 NXP Semiconductors ...
Page 224: ...Instruction Set Summary MC9S08PA4 Reference Manual Rev 5 08 2017 224 NXP Semiconductors ...
Page 232: ...Functional Description MC9S08PA4 Reference Manual Rev 5 08 2017 232 NXP Semiconductors ...
Page 258: ...FTM Interrupts MC9S08PA4 Reference Manual Rev 5 08 2017 258 NXP Semiconductors ...
Page 294: ...Functional description MC9S08PA4 Reference Manual Rev 5 08 2017 294 NXP Semiconductors ...
Page 398: ...Resets MC9S08PA4 Reference Manual Rev 5 08 2017 398 NXP Semiconductors ...
Page 400: ...MC9S08PA4 Reference Manual Rev 5 08 2017 400 NXP Semiconductors ...