STR720 datasheet(118/401 Pages) STMICROELECTRONICS

部件名	STR720

功能描述	ARM720T 16/32-BIT MCU WITH 16K RAM, USB, CAN, 3 TIMERS, ADC, 6 COMMUNICATIONS INTERFACES

PDF	401 Pages

Scroll/Zoom	100%

制造商	STMICROELECTRONICS [STMicroelectronics]

网页	http://www.st.com

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118 / 401 page

STR720 - EXTERNAL MEMORY INTERFACE (EMI)

118/401

11.3.2

Write Access Examples

In the Figure 11 shown below, a 16-bit write is being performed. The external bus width is also

16 bits. As can be seen from the diagram, all 2 external write strobes are asserted for the

duration of the write cycle. This is a one-cycle write and takes 5 AHB_CLK cycles to complete

(C_LENGTH = 3). The 1 LSB of the external address is not modified since it is a 16-bit

external bus.

11.3.3

Read Access Examples

The diagram in Figure 12 shows a basic READ operation. In the case of a READ only 1

external read strobe is required (ERDN). In this example, a 32-bit read is being performed on

the AHB but since the external bus size is 16 bits, it is necessary for the EMI peripheral to

perform 2 successive read operations. The results from the 1st read operation are latched

Figure 11. 16-bit write cycle

AHB_CLK

C_Length[2:0]

Ecs0n

Ewr0n

Ewr1n

Eadd[21:0]

Edata[15:0]

Erdn

(Output)

AHB address[22:1]

0x3

Access Length (3 Wait States)

Data

STR720 数据表(PDF) 118 Page - STMicroelectronics