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MOTOROLA M68040 USER’S MANUAL 7- 5
A0
A1
SIZ0
SIZ1
UPPER UPPER DATA SELECT
D31–D24
UPPER MIDDLE DATA SELECT
D23–D16
LOWER MIDDLE DATA SELECT
D15–D8
LOWER LOWER DATA SELECT
D7–D0
PAL16L8
U1
MC68040 Byte Data Select Generation.
Motorola Worldwide Marketing Training Organization
A0 A1 SIZ0 SIZ1 NC NC NC NC NC GND NC UUD UMD LMD LLD
NC NC NC NC VCC
/UUD = /A0 * /A1 
+ /SIZ1 * /SIZ0 
+ SIZ1 * SIZ0
; directly addressed, any size
; enable every byte for long word size
; enable every byte for line size
; directly addressed, any size
; word aligned, size is word or line
; enable every byte for long word size
; enable every byte for line size
; directly addressed, any size
; enable every byte for long word size
; enable every byte for line size
; directly addressed, any size
; word aligned, word or line size
; enable every byte for long word size
; enable every byte for line size
/UMD = A0 * /A1 
+ /A1 * /SIZ1 
+ SIZ1 * SIZ0
+ /SIZ1 * /SIZ0
/LMD = /A0 * /A1 
+ /SIZ1 * /SIZ0 
+ SIZ1 * SIZ0
/LLD = A0 * /A1 
+ /A1 * /SIZ1 
+ SIZ1 * SIZ0
+ /SIZ1 * /SIZ0
Figure 7-4. Byte Enable Signal Generation and PAL Equation
A brief summary of the bus signal encodings for each access type is listed in Table 7-2.
Additional information on the encodings for the M68040 signals can be found in Section 5
Signal Description.
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