System Considerations
MC1321x Reference Manual, Rev. 1.6
3-6
Freescale Semiconductor
•
MCU PTE5/SPSCK1 output drives modem SPICLK.
•
MCU PTE2/SS1 output drives modem CE.
The use and programming of the SPI command channel is described in
3.4.4
Modem Control Signals
The modem requires two additional input signals that are controlled by the MCU GPIO:
•
ATTN input controlled by PTD0 (pin 47) - The ATTN is an active low attention signal that is used
wake the modem from Hibernate or Doze Mode. The MCU GPIO PTD0 must be programmed as
an output and controls this input
•
RXTXEN input is controlled by PTD1 - The RXTXEN is an active high input used to enable
transmit, receive, and CCA operations in the modem. The MCU GPIO PTD1 must be programmed
as an output and controls this input
3.4.5
Modem Status Signals
The modem has two signals that provide real-time status 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. The MCU
GPIO PTE7 must be programmed as an input to monitor this signal. The modem GPIO1 signal can
also be used as a general purpose IO as long as there is no conflict with the MCU GPIO PTE7
•
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. The MCU GPIO PTE6
must be programmed as an input to monitor this signal. The modem GPIO2 signal can also be used
as a general purpose IO as long as there is no conflict with the MCU GPIO PTE6
3.5
Clock Sources
The MC321x device allows for a wide array of system clock configurations:
•
Pins are provided for a separate external clock source for the CPU. The external clock source can
by derived from a crystal oscillator or from an external clock source
•
Pins are provides for a 16 MHz crystal for the modem clock source
•
The modem crystal oscillator frequency can be trimmed through programming to maintain tight
tolerances required by the 802.15.4 Standard
•
The modem provides a CLKO programmable frequency clock output that can be used as an
external source to the CPU. As a result, a single crystal system clock solution is possible
•
Out of reset, the MCU uses an internally generated clock (approximately 8-MHz) for start-up. This
allows recovery from stop or reset without a long crystal start-up delay
•
The MCU contains an internal clock generator (which can be trimmed) that can be used to run the
MCU for low power operation
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