8XC251SA, SB, SP, SQ USER’S MANUAL
13-20
13.8.2 Example 2: RD1:0 = 01, 17-bit Bus, External Flash and RAM
In this example, an 80C251SB operates in page mode with a 17-bit external address bus inter-
faced to 64 Kbytes of flash memory for code storage and 32 Kbytes of external RAM (Figure
13-19). The 80C251SB is configured so that PSEN# is asserted for all reads, and RD# functions
as A16 (RD1:0 = 01). Figure 13-20 shows how the external flash and RAM are addressed in the
internal address space. Addresses 0420H–7FFFH in external RAM are addressed in region 00:.
On-chip data RAM (1056 bytes) occupies the lowest addresses in region 00:.
Figure 13-19. Bus Diagram for Example 2: 80C251SB in Page Mode
PSEN#
80C251SB
A4148-01
WR#
RAM
(32 Kbytes)
OE#
FLASH
(64 Kbytes)
OE#
WE#
WE#
CE#
CE#
A15:8/D7:0
A15:8
P2
P0
EA#
D7:0
A15:8
A7:0
A15:8
A7;0
D7:0
A16
A7:0
Latch
Data
Code
Содержание 8XC251SA
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Страница 3: ...May 1996 8XC251SA 8XC251SB 8XC251SP 8XC251SQ Embedded Microcontroller User s Manual...
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Страница 19: ...1 Guide to This Manual...
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Страница 31: ...2 Architectural Overview...
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Страница 41: ...3 Address Spaces...
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Страница 63: ...4 Device Configuration...
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Страница 81: ...5 Programming...
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Страница 103: ...6 Interrupt System...
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Страница 121: ...7 Input Output Ports...
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Страница 133: ...8 Timer Counters and Watchdog Timer...
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Страница 153: ...9 Programmable Counter Array...
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Страница 171: ...10 Serial I O Port...
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Страница 187: ...11 Minimum Hardware Setup...
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Страница 197: ...12 Special Operating Modes...
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Страница 207: ...13 External Memory Interface...
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Страница 239: ...14 Programming and Verifying Nonvolatile Memory...
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Страница 251: ...A Instruction Set Reference...
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Страница 391: ...B Signal Descriptions...
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Страница 401: ...C Registers...
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Страница 437: ...Glossary...
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Страница 447: ...Index...
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