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Boot Loader
4-19
Memory and I/O Spaces
Figure 4–10. Program Code Transferred From 8-Bit EPROM to 16-Bit RAM
8-Bit EPROM 16-Bit RAM
Address 7 0 Address 15 8 7 0
8000h Destination
h
= 00h 0000h Word1
h
Word1
l
8001h Destination
l
= 00h • Word2
h
Word2
l
8002h Length N
h
••. •
8003h Length N
l
•• •
8004h Word1
h
nnnEh • •
8005h Word1
l
nnnFh Wordn
h
Wordn
l
8006h Word2
h
8007h Word2
l
••
••
••
nnnEh Wordn
h
nnnFh Wordn
l
The ’C2xx fetches its interrupt vectors from program-memory locations
0000h–003Fh (the reset vector is fetched from 0000h). Make sure that the in-
terrupt vectors are stored at the top of the EPROM, so that they will be trans-
ferred to addresses 0000h–003Fh in the RAM (see Figure 4–11). Each inter-
rupt vector is a branch instruction, which requires four 8-bit words, and there
is space for 32 interrupt vectors. Therefore, the first 128 words to be trans-
ferred from the EPROM should be the interrupt vectors.