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80X CompactFlash Card

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5.2 Contiguous I/O Mapped Addressing

When the system decodes a contiguous block of I/O registers to select the CompactFlash Storage Card, the registers are
accessed in the block of I/O space decoded by the system as follows:

Table: Contiguous I/O Decoding

Notes:

1) Register 0 is accessed with -CE1 low and -CE2 low (and A0 = Don’t Care) as a word register on the combined Odd Data Bus and

Even Data Bus (D15-D0). This register may also be accessed by a pair of byte accesses to the offset 0 with -CE1 low and -CE2 high.
Note that the address space of this word register overlaps the address space of the Error and Feature byte-wide registers that lie at
offset

1. When accessed twice as byte register with -CE1 low, the first byte to be accessed is the even byte of the word and the second byte

accessed is the odd byte of the equivalent word access.

A byte access to register 0 with -CE1 high and -CE2 low accesses the error (read) or feature (write) register.

2) Registers at offset 8, 9 and D are non-overlapping duplicates of the registers at offset 0 and 1.

Register 8 is equivalent to register 0, while register 9 accesses the odd byte. Therefore, if the registers are byte accessed in the

order 9 then 8 the data shall be transferred odd byte then even byte.

Repeated byte accesses to register 8 or 0 shall access consecutive (even than odd) bytes from the data buffer. Repeated word

accesses to register 8, 9 or 0 shall access consecutive words from the data buffer. Repeated byte accesses to register 9 are not
supported. However, repeated alternating byte accesses to registers 8 then 9 shall access consecutive (even then odd) bytes from the
data buffer. Byte accesses to register 9 access only the odd byte of the data.

3) Address lines that are not indicated are ignored by the CompactFlash Storage Card for accessing all the registers in this table.