System Considerations
MC1321x Reference Manual, Rev. 1.6
3-12
Freescale Semiconductor
The BKGD pin is used primarily for background debug controller (BDC) communications using a custom
protocol that uses 16 clock cycles of the target MCUs BDC clock per bit time. The target MCUs 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 speed-up 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.
3.8
MC1321x GPIO (Mixed I/O from Modem and MCU)
The MC1321x SiP supports a total of 41 GPIO pins that originate from both the modem and the MCU:
•
Five package pins are GPIO from the modem (GPIO3-GPIO7) and can be used as inputs or outputs
•
Two package pins can be used as GPIO from either the MCU or the modem because they are
connected internally between the MCU and modem. However, they are more commonly used as
modem status bits to the MCU
— GPIO1/Out_of_Idle output drives PTE7 (pin 44) - The modem GPIO1 signal can optionally be
programmed as an “out-of-idle” indicator for monitoring RX, TX, or CCA operation
— GPIO2/CRC_Valid output drives PTE6 (pin 43) - The modem GPIO2 signal can optionally be
programmed as an “CRC valid” indicator for monitoring an RX operation
•
Thirty-four MAXIMUM additional MCU GPIO are available for use in the SiP package. The
actual MCU hardware supports a total of 56 GPIO signals in 7 ports, however, due to package
limitations and internal interconnects only the stated 34 can be used with the following limitations
— If a crystal is used with the MCU, PTG1/XTAL and PTG2/EXTAL pins cannot be used as
GPIO. These are available only using the internal clock reference
— If CLKO is used to drive the external clock source to the MCU, EXTAL is not available as
GPIO
— PTG0/BKGD/MS is not commonly used as GPIO because it is dedicated to the MCU debug
port (BDM)
— In the most common clock configuration (CLKO driving EXTAL and PTG0/BKGD/MS used
with the debug port), there are 32 usable MCU GPIO
3.8.1
MCU GPIO Characteristics
The internal MCU GPIO hardware consists of 8 ports with 7 signals per port for a total of 56 signals (not
all are available on the package). There are 55 GPIO and one output only (PTG0_BKGD_MS).
Immediately after MCU reset, all 55 of the GPIO pins are configured as high-impedance general-purpose
inputs with internal pull-up devices disabled.
Содержание freescale semiconductor MC13211
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