Vi-2-1. Cpu - Canon A-200 series Service Manual

- - -
- - -
VI-2-1. CPU
The A-200 uses the 8086 16-bit microprocessor in maximum mode.
Figure 6-3 shows the pin assignment and pin description for the 8086 operated in maximum mode.
• AD15 - ADO (Address and Data) ..... inputs/outputs in three states
These lines construct the memory and I/O address bus (T1) and the data bus (T2, T3, TW, T4).
The AO signal acts similar to the BHE signal to the lower byte (DO - 07) data bus. If one byte
is to be sent to the lower bytes of the bus in memory access or I/O control operation, the AO
terminal becomes lOW during the period of T1.
These terminals keep high impedance during interrupt acknowledge and hold acknowledge cy ­
cle of local bus.
• A19/S6, A18/S5, A17/S4, A16/S3 (Address/Status) ..... outputs in three states
These lines output upper 4 bits of data in memory accessing during the period of T1. When I/O
operation, these lines are all lOW. During T2, T3, TW and T4 in memory access or I/O control
operation, a status information is output. The status of the interrupt enable flag 1 F (S5) is reset
with the beginning of each ClK cycle (T1). S6 is always zero.
A17/S4, A16/S3 are encoded as follows:
A17/S4
A16/S3
0
0 Alternate Data
0 1 Stack
0 Code or None
1 Data
Above information shows which relocation register is used for data accessing. Impedance of these
lines keep high during hold acknowledge cycle of the local bus.
GND
Vee
AD14
AD15
AD13
A 16/S3
AD12 A 17/S4
AD11
A18/S5
AD10
A 19/56
AD9
BHE/S7
AD8
MN/MX
AD7
RD
AD6 RQ/GTO
AD5
RQ/GT1
AD4 lOCK
AD3 S2
AD2 S1
AD1 SO
ADO
QSO
NMI OSl
INTR
TEST
ClK
READY
GND RESET
Figure
6-3
48