The format of the BIU flag word is shown in Figure 6-6. Only the 16 most significant bits
in the BIU flag word are defined; the undefined bits are written as ones during save
operations and ignored during restore operations.
The definitions of the 16 flag bits are"
Bits 16-19
These bits contain internal state information about the CU and should
not be modified.
Bits 20-23
These bits are set when valid data is contained in the operand register
image of the state frame. There is one flag bit for each byte in the
32-bit operand register image; if a bit is one, there is valid data in the
corresponding byte. If a bit is zero, the data in the corresponding byte
is assumed to be invalid. These bits can be used to qualify the image
of the operand register and should not be modified.
Bits 24-25
These bits contain internal state information about the CU and should
not be modified.
Bit 26
This bit indicates that the FPCP has completed any necessary operand
conversions and is ready to write an operand to memory. If this bit is a
zero, an operand transfer to memory is pending. This bit should not be
modified.
INTERNAL STATE INFORMATION
(MC68882
ONLY)
III
26 23 20
IIIIIIIIIII
II--
15 7 0
OPERAND REGISTER BITS 24-31 VAUO
OPERAND REGISTER BITS 16-23 VALID
OPERAND REGISTER BITS 8-15 VALID
OPERAND REGISTER BITS 0-7 VAUD
OPERAND TO MEMORY MOVE PENDING
FLOATING-POINT EXCEPTION PENDING
ACCESS OF OPERAND REGISTER EXPECTED
PENDING INSTRUCTION OR ACCESS TYPE
IM~Tfll IPTInM P~Nnl~Jc
PROTOCOL VIOLATION PENDING
UNDEFINED. RESERVEO (! WHEN READ)
Figure 6-6. BIU Flag Format
MC68881/MC68882 USER'S MANUAL
FREESCALE
6-33
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