AN2727 Freescale Semiconductor / Motorola, AN2727 Datasheet - Page 12

• Manufacturer Part Number: AN2727
• Description: Designing Hardware for the HCS12 D-Family
• Manufacturer: Freescale Semiconductor / Motorola

Pin Considerations Collection – Control
Port E.0 : XIRQ
PE0 is a general purpose input pin and optional non-maskable interrupt request input that can provide a
means of applying asynchronous interrupt requests. This will wake up the MCU from STOP or WAIT
mode. This interrupt input is active low level sensitive.
BKGD / MODC
The BKGD/TAGHI/MODC pin is used as a pseudo open-drain pin for the background debug
communication link.
The state of this pin is copied to the MODC bit at the rising edge of RESET. This pin controls whether the
device enters special mode on release of reset. Internally, it has a permanently enabled weak pull-up, to
ensure that it enters normal mode if not connected. This pull-up may not be strong enough to ensure
adequate rise times for BDM communication with all development tools. If BDM support is required it is
recommended to fit an external pull-up resistor. See
Easy access to the RESET, BKGD, 0V and VDD5 signals can facilitate debugging. It is highly
recommended to include a standard 6-pin header in all design layouts to support in-system debug and
reprogramming; the header need not be populated for production. See
Connection.
XFC
To use the PLL, an appropriate filter network should be fitted between the XFC pin and VDDPLL. See
HCS12
Fitting PLL filter components to all designs, whether they use the PLL or not, can be a good idea where
BDM tools capable of high speed programming are being used.
12
PLL.
If an application requires STOP mode, this pin must be used with care
(whether it is the source of the wake from STOP signal or not). Behavior of
the STOP instruction is directly linked to the XIRQ functionality. The X bit in
the CPU condition codes register masks the XIRQ interrupt (preventing the
interrupt vector from being taken) but it does not prevent the XIRQ pin from
waking the MCU from STOP mode. As XIRQ is level sensitive, while this
pin is low the MCU will not enter STOP mode.
Designing Hardware for the HCS12 D-Family, Rev. 0
CAUTION
BKGD Pull-up
Value.
Standard Serial Debug Interface
Freescale Semiconductor