EM78451AP EMC [ELAN Microelectronics Corp], EM78451AP Datasheet - Page 42

• Manufacturer Part Number: EM78451AP
• Description: 8-Bit Microcontroller
• Manufacturer: EMC [ELAN Microelectronics Corp]

EM78451
8-Bit Microcontroller
38 •
4.9 Oscillator
/IRQn
RESET
The flag in the Interrupt Status Register (R3F) is set regardless of the status of its mask
bit or the execution of ENI instruction. Note that reading R3F will obtain the output of
logic AND of R3F and IOCF (refer to Fig. 17). The RETI instruction will exit interrupt
routine and enables the global interrupt (execution of ENI instruction).
When an interrupt is generated by INT instruction (if enabled), it causes the next
instruction to be fetched from address 002H.
4.9.1 Oscillator Modes
The EM78451 can operate in four different oscillator modes. There are high XTAL
(HXT) oscillator mode, low XTAL (LXT) oscillator mode, External RC oscillator mode
(ERC), and Internal C、External R oscillator mode. User can select one of them by
programming MS, RCT, IRC, HLF and HLP in the Code Option Register. Table 9
depicts how these three modes are defined.
Table 9 Oscillator Modes by MS, RCT.
High XTAL Oscillator
Low XTAL Oscillator
External RC Oscillator
External R and Internal C Oscillator
R3F
CLK
D
C
L
R
P
Q
Q
Mode
Fig. 17 Interrupt input circuit
IOCF
Q
Q
C
RFW R
R
L
P
CLK
IOCF RD
D
(This specification is subject to change without further notice)
RFRD
IOCFW R
IRQn
IRQm
Product Specification (V1.2) 05.27.2004
MS
1
1
0
0
ENI/DISI
RCT
IOD
X
X
1
0
interrupt
HLF
X
X
1
0