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3.7.1
Extended Intelligent I/O Service Descriptor (ISD)
The extended intelligent I/O service descriptor exists between "000100
in built-in RAM, and consists of the following items:
• Data transfer control data
• Status data
• Buffer address pointer
■ Extended Intelligent I/O Service Descriptor (ISD)
Figure 3.7-2 shows the configuration of the extended intelligent I/O service descriptor.
Figure 3.7-2 Extended Intelligent I/O Service Descriptor Configuration
+ 8 × ICS
000100
H
ISD start address
■ Data Counter (DCT)
This is a 16-bit register that works as a counter corresponding to the number of data items transferred. This
counter is decremented by one before data transfer. EI
Figure 3.7-3 is a diagram of the data counter configuration.
bit
15
14
13
12
B15 B14 B13 B12 B11 B10 B09 B08 B07 B06 B05 B04 B03 B02 B01 B00
High-order 8 bits of data counter (DCTH)
Low-order 8 bits of data counter (DCTL)
High-order 8 bits of I/O address pointer (IOAH)
Low-order 8 bits of I/O address pointer (IOAL)
2
EI
OS status (ISCS)
High-order 8 bits of buffer address pointer (BAPH)
Medium-order 8 bits of buffer address pointer (BAPM)
Low-order 8 bits of buffer address pointer (BAPL)
Figure 3.7-3 Data Counter Configuration
11
10
9
8
7
2
OS is terminated when this counter reaches "0".
6
5
4
3
2
CHAPTER 3 INTERRUPTS
" and "00017F
H
"H"
"L"
1
0
DCT
(Undefined when reset)
"
H
73
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