Freescale Semiconductor Eval, Demo and Development Board for MCF51MM256 TWR-MCF51MM TWR-MCF51MM Datenbogen

Freescale Semiconductor

39

o

A multi-function external bus interface called Mini-FlexBus is provided with basic functionality to 
interface to slave-only devices up to a maximum bus frequency of 

25.1666 MHz

. It can be directly connected 

to asynchronous or synchronous devices such as external boot ROMs, flash memories, gate-array logic, or 
other simple target (slave) devices with little or no additional circuitry. For asynchronous devices a simple 
chip-select based interface can be used. 

All processor bus timings are synchronous; that is, input setup/hold and output delay are given in respect 
to the rising edge of a reference clock, MB_CLK. The MB_CLK frequency is half the internal system bus 
frequency. 

The following timing numbers indicate when data is latched or driven onto the external bus, relative to the 
Mini-FlexBus output clock (MB_CLK). All other timing relationships can be derived from these values.

6 Crystal start-up time 

4

 • Low range, low gain (RANGE = 

0, HGO = 0)

t

CSTL-LP

—

200

—

ms

D

 • Low range, high gain 

(RANGE = 0, HGO = 1)

t

CSTL-HG

O

—

400

—

D

 • High range, low gain 

(RANGE = 1, HGO = 0)

5

t

CSTH-LP

—

5

—

D

 • High range, high gain 

(RANGE = 1, HGO = 1)

5

t

CSTH-HG

O

—

15

—

D

1

Data in Typical column was characterized at 3.0 V, 25C or is typical recommended value.

2

When MCG is configured for FEE or FBE mode, input clock source must be divisible using RDIV to within the range of 31.25 kHz to 39.0625 kHz.

3

When MCG is configured for PEE or PBE mode, input clock source must be divisible using RDIV to within the range of 1 MHz to 2 MHz.

4

This parameter is characterized and not tested on each device. Proper PC board layout porcedures must be followed to achieve specifications.

5

4 MHz crystal.

°

MCU

EXTAL

 XTAL

R

S

C

2

Crystal or Resonator 

R

F

C

1