RESET
7902 Group User’s Manual
4-3
Bit name
Bit
Processor mode register 0 (Address 5E16)
Function
At reset
R/W
Processor mode bits
External bus cycle select bit 0
(Note 2)
Interrupt priority detection time
select bits
Software reset bit
Clock
φ1 output select bit
b7 b6 b5 b4 b3 b2 b1 b0
Notes 1: When the Vss-level voltage is applied to pin MD0, this bit is “0”; when the Vcc-level voltage is applied to pin MD0, this bit
is “1.” (Fixed to “1.”)
2: These bits are valid for the external area except for area CSi. Regardless of these bits’ contents, the bus cycle of area CSi
is decided by the corresponding area CSi bus cycle select bits 0, 1 (bits 0, 1 at addresses 8016, 8216, 8416, 8616, and bit 3
at addresses 8116, 8316, 8516, 8716).
3: When the Vss-level voltage is applied to pin MD0, this bit is “0”; when the Vcc-level voltage is applied to pin MD0, this bit
is “1.”
0 0 : Single-chip mode
0 1 : Memory expansion mode
1 0 : Microprocessor mode
1 1 : Do not select.
b1 b0
0 0 : 7 cycles of fsys
0 1 : 4 cycles of fsys
1 0 : 2 cycles of fsys
1 1 : Do not select.
b5 b4
The microcomputer is reset by writing “1” to this
bit. The value is “0” at reading.
0 :
φ1 output is disabled. (P41 functions as a
programmable I/O port pin.)
1 :
φ1 output is enabled. (P41 functions as a clock φ1
output pin.)
0
1
2
3
4
5
6
7
0
(Note 1)
0
1
0
(Note 3)
RW
WO
RW
0 0 : 1
φ + 1φ
0 1 : 1
φ + 2φ
1 0 : 1
φ + 3φ
1 1 : 2
φ + 2φ
b2
b3
0 0 : 2
φ + 3φ
0 1 : 2
φ + 4φ
1 0 : 3
φ + 3φ
1 1 : 3
φ + 4φ
b2
b3
(External bus cycle select
bit 1 = 0)
(External bus cycle select
bit 1 = 1)
Fig. 4.1.2 Structure of processor mode register 0
4.1.2 Software reset
The microcomputer initializes pins, CPU, and SFR area just as in the case of hardware reset (Refer to
sections “4.2 Pin state” and “4.3 State of internal area”) by writing “1” to the software reset bit. (See
Figure 4.1.2.)
After initialization completed, the microcomputer performs “Internal processing sequence after reset.” (Refer
to section “4.4 Internal processing sequence after reset.”) After that, it executes a program beginning
with the address which has been set into the reset vector addresses (FFFE16 and FFFF16).
4.1 Reset operation