mcf51ac256a Freescale Semiconductor, Inc, mcf51ac256a Datasheet - Page 206

• Manufacturer Part Number: mcf51ac256a
• Description: Mcf51ac Flexis
• Manufacturer: Freescale Semiconductor, Inc

FlexTimer Module (FTMV1)
11.2
Table 11-1
11.2.1
When an external clock is included, it can be shared with the same pin as any FTM channel or it can be
connected to a separate input pin. Refer to the I/O pin descriptions in full-chip specification for the specific
chip implementation.
If the external clock signal shares the same pin as a channel I/O pin, then this channel pin will not be
available for channel I/O functions when the external clock source is selected. It is the user’s responsibility
to avoid conflicting settings such as this.
The external clock source is synchronized in the FTM. The system clock clocks the synchronizer, so the
frequency of the external source must be no more than one-fourth the frequency of the system clock, to
meet Nyquist criteria and allow for jitter.
11.2.2
Each FTM channel is associated with an I/O pin on the MCU. The function of this pin depends on the
channel configuration. The FTM pins are shared with general purpose I/O pins, where each pin has a port
data register bit, and a data direction control bit, and the port has optional passive pullups which may be
enabled whenever a port pin is acting as an input.
Immediately after reset, no FTM functions are enabled, so all FTM channels pins revert to general purpose
I/O control. The FTM channels pins also revert to general purpose I/O control when (CLKS = 00) or
(ELSnB:ELSnA = 0:0).
11-6
Signal Description
shows the user-accessible signals for the FTM.
1
2
FTMxCLK — FTM External Clock
FTMxCHn — FTM Channel (n) I/O Pin(s)
When preset, this signal can share any channel pin; however depending upon full-chip
implementation, this signal could be connected to a separate external pin.
n=channel number (0 to 7)
FTMxCHn
FTMxCLK
Name
MCF51AC256 ColdFire Integrated Microcontroller Reference Manual, Rev. 5
1
2
FTM x External Clock - FTM external clock which may be selected to drive the
FTM counter
FTM x channel (n) - I/O pin associated with FTM channel (n)
Table 11-1. Signal Properties
Function
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