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CHAPTER 4 BUS INTERFACE
❍ 8-bit bus
Figure 4.4-8 External bus access in big-endian mode (8-bit bus)
(A) Word access
(a)PA1/PA0='00'
(1) Output A1/A0 = '00'
(2) Output A1/A0 = '01'
(3) Output A1/A0 = '10'
(4) Output A1/A0 = '11'
MSB LSB
(1)
00
(2)
01
(3)
10
(4)
11
8bit
(B) Half-word access
(a)PA1/PA0='00'
(1) Output A1/A0 = '00'
(2) Output A1/A0 = '01'
(1)
00
(2)
01
10
11
(C) Byte access
(a)PA1/PA0='00'
(1) Output A1/A0 = '00'
(1)
00
01
10
11
PA1/PA0: the lower two bits of the address specified by a program
Output A1/A0: the lower two bits of the address to be output
: Leading byte position of an address to be output
: Data byte position to be accessed
+
: Bus access count
(1) to (4)
120
(b)PA1/PA0='01'
(1) Output A1/A0 = '00'
(2) Output A1/A0 = '01'
(3) Output A1/A0 = '10'
(4) Output A1/A0 = '11'
(1)
00
(2)
01
(3)
10
(4)
11
(b)PA1/PA0='01'
(1) Output A1/A0 = '00'
(2) Output A1/A0 = '01'
(1)
00
(2)
01
10
11
(b)PA1/PA0='01'
(1) Output A1/A0 = '01'
00
(1)
01
10
11
(c)PA1/PA0='10'
(1) Output A1/A0 = '00'
(2) Output A1/A0 = '01'
(3) Output A1/A0 = '10'
(4) Output A1/A0 = '11'
(1)
00
(2)
01
(3)
10
(4)
11
(c)PA1/PA0='10'
(1) Output A1/A0 = '10'
(2) Output A1/A0 = '11'
00
01
(1)
10
(2)
11
(c)PA1/PA0='10'
(1) Output A1/A0 = '10'
00
01
(1)
10
11
(d)PA1/PA0='11'
(1) Output A1/A0 = '00'
(2) Output A1/A0 = '01'
(3) Output A1/A0 = '10'
(4) Output A1/A0 = '11'
(1)
00
(2)
01
(3)
10
(4)
11
(d)PA1/PA0='11'
(1) Output A1/A0 = '10'
(2) Output A1/A0 = '11'
00
01
(1)
10
(2)
11
(d)PA1/PA0='11'
(1) Output A1/A0 = '11'
00
01
10
(1)
11
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