AN2647 datasheet(16/34 Pages) STMICROELECTRONICS

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Interfacing with asynchronous memory

AN2647

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1.2.3

BCLK clock frequency

The EMI bus clock (BCLK) can be configured to have the same frequency or half the

frequency of the AHB bus clock (HCLK). The maximum BCLK frequency supported by the

EMI bus is specified in the STR91xFA Data Sheet.

The BCLK frequency is controlled by the EMIRATIO bit in the SCU_CLKCNTR register to

divide the HCLK by 1 or by ½.

The BCLK pin is available as an output in BGA package only. The BCLK clock is enabled by

setting bit 1 in the SCU_EMI register

Table 4.

EMI port configuration

Port7

Port8 and 9

Port0

(P0.4-P0.7)

Port5

(P5.4-P5.7)

EMI bus signals:A16-

A23 or CS0-CS3

(Multiplexed bus)

A0-A7

(Non-multiplexed bus)

EMI bus

signals:AD0-AD15

(Multiplexed bus)

D0-D7 & A8-A15

(Non-multiplexed

bus)

EMI bus signals:

CS0-CS3

EMI bus signals:

CS0-CS3

Multiplexed Bus

Port Register

configuration

SCU_GPIOOUT7

[13:0]=to ALT 2 function

SCU_GPIOOUT7

[15:14]=to ALT 3 function

SCU_GPIOOUT7=0XEA

(A16-A23 are pin

selectable, you only need

to configure the pins that

are required)

SCU_EMI Register

GPIOEMI bit =0

(Set ports 8 and 9 as

EMI AD bus)

SCU_GPIOOUT0

[8:15]= to ALT 3

function.

SCU_GPIOOUT0=

0XFFxx

(CS0-3 are pin

selectable, you only

need to configure the

pins that are

required)

SCU_GPIOOUT0

[8:15]= to ALT 3

function.

SCU_GPIOOUT0=

0XFFxx.

(CS0-3 are pin

selectable, you only

need to configure

the pins that are

required)

SCU_GPIOTYPE7

=0X00 (push-pull)

SCU_GPIOTYPE8,9

=0X00 (push-pull)

SCU_GPIOTYPE0

=0X0x (push-pull)

SCU_GPIOTYPE5

=0X0x (push-pull)

EMI_Multiplexed mode

bit in SCU_SCR0 [6]=0

Non-Multiplexed

Bus Port Register

Configuration

SCU_GPIOOUT7

[13:0]=to ALT 2 function

SCU_GPIOOUT7

[15:14]=to ALT 3 function

SCU_GPIO=0XEAAA

SCU_EMI Register

GPIOEMI bit =1

(set ports 8 as data

bus and 9 as

address bus)

Same as Multiplexed

bus

Same as

Multiplexed bus

SCU_GPIOTYPE7

=0X00 (push-pull)

SCU_GPIOType8,9

=0X00 (push-pull)

EMI_Multiplexed mode

bit in SCU_SCR0 [6]=1

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