Table 2-2. Status Field Encoding
80386
Status Bit
10 9 8 7 6 5 4 3 2 1 0
Cycle Type
Interrupt Acknowledge
x x x x x x x x 0 0 0
I/O Read
x x x x x x x x 0 1 0
I/O Write
x x x x x x x x 0 1 1
Opcode Fetch
x x x x x x x x 1 0 0
Halt/Shutdown
x x x x x x x x 1 0 1
Memory Read
x x x x x x x x 1 1 0
Memory Write
x x x x x x x x 1 1 1
Valid Bytes in Transfer
(from BE0# through BE3# )
Double Word (all bytes valid)
x x x 0 0 0 0 x x x x
Higher 3 Bytes
x x x 0 0 0 1 x x x x
High Word
x x x 0 0 1 1 x x x x
Byte 3
x x x 0 1 1 1 x x x x
Lower 3 Bytes
x x x 1 0 0 0 x x x x
Middle Word
x x x 1 0 0 1 x x x x
Byte 2
x x x 1 0 1 1 x x x x
Low Word
x x x 1 1 0 0 x x x x
Byte 1
x x x 1 1 0 1 x x x x
Byte 0
x x x 1 1 1 0 x x x x
Size of Transfer
16-bit Transfer
x x 0 x x x x x x x x
32-bit Transfer
x x 1 x x x x x x x x
Note: X = don’t care. The actual status field is a 15-bit field; however, bits 11 through
14 are not shown since they are "don’t cares."
HP E2444A
Analyzing the Intel 80386DX/DXL
80386DX/DXL Preprocessor Interface
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