MAC7200 datasheet(785/976 Pages) FREESCALE

785 / 976 page

Functional Description

MAC7200 Microcontroller Family Reference Manual, Rev. 2

Freescale Semiconductor

707

In order to guarantee coherent access, reading UCAn disables transfers between B2 and B1. These

transfers are disabled until the next read of the UCBn register. Reading the UCBn register re-enables

transfers from B2 to B1, to take effect at the next transfer event, as described above.1

Triggering of the counter clock (input event) is done by a rising or falling edge or both edges on the input

pin. The polarity of the triggering edge is selected by the EDSEL and EDPOL bits in UCCRn register.

For continuos operation mode (MODE[0] cleared), the counter is cleared on the next input event after a

FLAG generation and continues to operate as described above.

For single shot operation (MODE[0] set), the counter is not cleared or incremented after a FLAG

generation, until a new writing operation to register A is performed.

Figure 32-23 and Figure 32-24 show how the Unified Channel can be used for continuos and single shot

pulse/edge accumulation mode.

Figure 32-23. Pulse/Edge Accumulation continuous mode example

1. If B1 was not updated due to B2 to B1 transfer being disabled after reading register UCAn, further UCAn and UCBn reads will

not return coherent data until a new bus capture is triggered to registers A2 and B2. This capture event is indicated by the

channel FLAG being asserted. If enabled, the FLAG also generates an interrupt.

$FFFFFF

$000000

UCCNTn1

Time

A1 Match

write to A1

selected counter bus

$000400

A1 value3

$001500

$xxxxxx

value4

$000400

$xxxxxx

value

$000090

$xxxxxx

value5

$001000

$xxxxxx

$001500

$000090

$007000

$001500

$007000

$001000

FLAG set event

A1 Match

$001500

input signal2

$001000

A1 events

no events

events

$000400

Notes:

4. UCAn = A2 (when reading)

5. UCBn = B1

3. UCAn = A1 (when writing)

2. After input filter

1. Cleared on the first input event after writing to register A1

$007000

MODE[0]= 0

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