Intel 8XC251SB, 8XC251SA, 8XC251SP, 8XC251SQ manual Example 7 RD10 = 01, 17-bit Bus, External Flash

Models: Embedded Microcontroller 8XC251SP 8XC251SA 8XC251SQ 8XC251SB

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8XC251SA, SB, SP, SQ USER’S MANUAL

13.8.7 Example 7: RD1:0 = 01, 17-bit Bus, External Flash

In this example, an 80C251SB operates in page mode with a 17-bit external address bus inter- faced to 128 Kbytes of flash memory (Figure 13-28). Port 2 carries both the upper address bits (A15:0) and the data (D7:0), while port 0 carries only the lower address bits (A7:0). The 80C251SB is configured for a single read signal (PSEN#). The 128 Kbytes of external flash are accessed via internal memory regions FE: and FF: in the internal address space.

80C251SB

 

FLASH

 

 

 

(128 Kbytes)

 

EA#

 

CE#

 

 

A16

A16

A16

 

 

 

 

 

 

 

Code

 

 

 

D7:0

 

 

P2

Latch

A15:8

 

 

 

A15:8/D7:0

A15:8

 

 

P0

 

A7:0

 

 

 

A7:0

 

 

WR#

PSEN#

 

OE#

WE#

A4151-01

Figure 13-28. Bus Diagram for Example 7: 80C251SB in Page Mode

13-30

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Intel 8XC251SB, 8XC251SA Example 7 RD10 = 01, 17-bit Bus, External Flash, Bus Diagram for Example 7 80C251SB in Page Mode