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TSC80251G2D-L16CE Datasheet(PDF) 11 Page - ATMEL Corporation |
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TSC80251G2D-L16CE Datasheet(HTML) 11 Page - ATMEL Corporation |
11 / 76 page 11 AT/TSC8x251G2D 4135D–8051–08/05 Address Spaces The TSC80251G2D derivatives implement four different address spaces: • On-chip ROM program/code memory (not present in ROMless devices) • On-chip RAM data memory • Special Function Registers (SFRs) • Configuration array Program/Code Memory The TSC83251G2D and TSC87251G2D implement 32 KB of on-chip program/code memory. Figure 4 shows the split of the internal and external program/code memory spaces. If EA# is tied to a high level, the 32-Kbyte on-chip program memory is mapped in the lower part of segment FF: where the C251 core jumps after reset. The rest of the program/code memory space is mapped to the external memory. If EA# is tied to a low level, the internal program/code memory is not used and all the accesses are directed to the external memory. The TSC83251G2D products provide the internal program/code memory in a masked ROM memory while the TSC87251G2D products provide it in an EPROM memory. For the TSC80251G2D products, there is no internal program/code memory and EA# must be tied to a low level. Figure 4. Program/Code Memory Mapping Note: Special care should be taken when the Program Counter (PC) increments: If the program executes exclusively from on-chip code memory (not from external mem- ory), beware of executing code from the upper eight bytes of the on-chip ROM (FF:7FF8h-FF:7FFFh). Because of its pipeline capability, the TSC80251G2D derivative may attempt to prefetch code from external memory (at an address above FF:7FFFh) and thereby disrupt I/O Ports 0 and 2. Fetching code constants from these 8 bytes does not affect Ports 0 and 2. When PC reaches the end of segment FF:, it loops to the reset address FF:0000h (for On-chip ROM/EPROM Code Memory Program/code Segments Program/code External Memory Space 32 KB EA# = 0 EA# = 1 32 KB 32 KB Reserved 64 KB 128 KB FF:FFFFh FF:8000h FF:7FFFh FF:0000h FE:FFFFh FE:0000h FD:FFFFh 01:FFFFh 01:0000h 02:0000h 00:FFFFh 00:0000h |
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