SPMC68CK338CPV14 datasheet(90/133 Pages) FREESCALE

90 / 133 page

MOTOROLA

MC68CK338

MC68CK338TS/D

The FCSM counter register is a read/write register. A read returns the current value of the counter. A

write loads the counter with the specified value. The counter then begins incrementing from this new

value.

6.8 Modulus Counter Submodule (MCSM)

The modulus counter submodule (MCSM) is an enhancement of the FCSM. The MCSM contains a 16-

bit modulus latch, a 16-bit loadable up-counter, counter loading logic, a clock selector, a time base bus

driver, and an interrupt interface. A modulus latch gives the additional flexibility of recycling the counter

at a count other than 64-Kbyte clock cycles. The state of the modulus latch is transferred to the counter

when an overflow occurs or when a user-specified edge transition occurs on an external input pin. In

addition, a write to the modulus counter simultaneously loads both the counter and the modulus latch

with the specified value. The counter then begins incrementing from this new value.

Three MCSMs are contained in the CTM6. Figure 21 shows a block diagram of the MCSM.

NOTE

In order to count, the MCSM requires the CPSM clock signals to be present. On

coming out of reset, the MCSM does not count internal or external events until the

prescaler in the CPSM starts running (when the software sets the PRUN bit). This

allows all counters in the CTM6 submodules to be synchronized.

Figure 21 MCSM Block Diagram

FCSM3CNT — FCSM Counter Register

$YFF41A

RESET:

INTERRUPT

CONTROL

CLOCK

INPUT PIN

CTMC

CTM MCSM BLOCK

16-BIT UP COUNTER

IL2

IL1

IL0

IARB3

COF

EDGE

TIME BASE BUSES

IL1

CLOCK

IN2

CLK1 CLK0

CLK2

OVERFLOW

BUS

CONTROL REGISTER BIT

CONTROL REGISTER BITS

6 CLOCKS (PCLKX) FROM PRESCALER

SUBMODULE BUS

SELECT

DETECT

MODULUS

CONTROL

MODULUS REGISTER

CONTROL REGISTER BITS

EDGEN EDGEP

EDGE

MODULUS LOAD

DETECT

INPUT PIN CTML

IN1

CONTROL REGISTER BITS

WRITE

BOTH

DRVA DRVB

CONTROL REGISTER BITS

TBBA

TBBB

MODULUS

CONTROL REGISTER BIT

LOAD INPUT

PIN CTML

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SPMC68CK338CPV14 Datasheet(PDF) 90 Page - Freescale Semiconductor, Inc

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