6
31
i
,°° -I
23
NULL
STATE FRAME
15
(UNOEFINEDI I
7 D
(RESERVE0}
I
$80
$O4
$O8
$0C
$10
$14
$18
31 23
VERSION NUMBER I
COMMANO/CQNOITION REGISTER
IDLE
STATE FRAME
15
$18
I
EXCEPTIONAL OPEPANO
(12 BYTES)
7 0
(RESERVEO)
(RESERVED)
OPEP,,AND REGISTER
8EU FLAGS
$00
$04
$08
$0C
SAC
SR0
$84
31 23
VERSION NUMBER .[
BUSY STATE FRAME
15 7 0
(~SEP~'E0)
INTERNAL REGISTERS
(180 BYTES)
Figure 6-4. MC68881 State Frame Formats
frames each contain 32 additional bytes, which store the CU internal state. Second, the
saved CU internal state is saved at the top of the frame, immediately following the format
word. This results in offsets to the APU information that are greater than those for cor-
responding data in the MC68881 state frames by $20. The null state frame consists only
of the format word in both coprocessors.
When an FSAVE instruction is executed, the format word is the first data item transferred
to the MPU, and the main processor uses the size value to perform the correct address
FREESCALE
6-30
MC68881/MC68882 USER'S MANUAL
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