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II CORE BLOCK: BCU (Bus Control Unit)
S1C33210 FUNCTION PART EPSON B-II-4-15
Ignored
15
Data bus
0#WRL
1
1
1
1
#WRH
X
X
X
X
A0
0
1
0
1
A1
0
0
1
1
No.
1
2
3
4
Byte 0
Ignored Byte 1
Ignored Byte 2
Ignored Byte 3
Byte 3 Byte 2 Byte 1 Byte 0
31 0
A[1:0]=10 A[1:0]=00A[1:0]=11 A[1:0]=01
80
14
888000
32
Bus operation
(X: Not connected/Unused)
Destination (general-purpose register)
Source (8-bit device)
Little-endian
Byte 3
15
Data bus
0#WRL
1
1
1
1
#WRH
1
1
1
1
A0
0
1
0
1
A1
0
0
1
1
No.
1
2
3
4
Ignored
Byte 2 Ignored
Byte 1 Ignored
Byte 0 Ignored
Byte 3 Byte 2 Byte 1 Byte 0
31 0
A[1:0]=01 A[1:0]=11A[1:0]=00 A[1:0]=10
80
41
888000
23
Bus operation
Destination (general-purpose register)
Source (8-bit device)
Big-endian
Figure 4.12 Word Data Reading from an 8-bit Device
Data retained
15 Data bus 0#WRL
0
0
#WRH
X
X
A0
0
1
A1
∗
∗
No.
1
2
Byte 0
Data retained Byte 1
Byte 3 Byte 2 Byte 1 Byte 0
31 0
A[1:0]=∗0A[1:0]=∗1
0
1
880
Source (general-purpose register)
Destination (8-bit device)
2
Bus operation
(X: Not connected/Unused)
Little-endian
Byte 1
15 Data bus 0#WRL
0
0
#WRH
0
0
A0
0
1
A1
∗
∗
No.
1
2
Data retained
Byte 0 Data retained
Byte 3 Byte 2 Byte 1 Byte 0
31 0
A[1:0]=∗1A[1:0]=∗0
0
2
880
Source (general-purpose register)
Destination (8-bit device)
1
Bus operation
(∗: Uniformly 1 or 0)
Big-endian
Figure 4.13 Half-word Data Writing to an 8-bit Device
Ignored
15 Data bus 0#WRL
1
1
#WRH
X
X
A0
0
1
A1
∗
∗
No.
1
2
Byte 0
Ignored Byte 1
Byte 1 Byte 0
31 0
A[1:0]=∗0A[1:0]=∗1
0
1
880
2
Bus operation
(X: Not connected/Unused)
Destination (general-purpose register)
Source (8-bit device)
Sign or Zero extension
Little-endian
Byte 1
15 Data bus 0#WRL
1
1
#WRH
1
1
A0
0
1
A1
∗
∗
No.
1
2
Ignored
Byte 0 Ignored
Byte 1 Byte 0
31 0
A[1:0]=∗1A[1:0]=∗0
0
2
880
1
Bus operation
Destination (general-purpose register)
Sign or Zero extension
Big-endian
(∗: Uniformly 1 or 0)
Figure 4.14 Half-word Data Reading from an 8-bit Device
Data retained
15 Data bus 0#WRL
0
#WRH
X
A0
∗
A1
∗
No.
1 Byte 0
Byte 3 Byte 2 Byte 1 Byte 0
31 0
A[1:0]=∗∗
0
1
8
Source (general-purpose register)
Destination (8-bit device)
Bus operation
(X: Not connected/Unused)
Little-endian
Byte 0
15 Data bus 0#WRL
1
#WRH
0
A0
∗
A1
∗
No.
1
Data retained
Byte 3 Byte 2 Byte 1 Byte 0
31 0
A[1:0]=∗∗
0
1
8
Source (general-purpose register)
Destination (8-bit device)
Bus operation
Big-endian
Figure 4.15 Byte Data Writing to an 8-bit Device