EM78P5840/5841/5842
8-bit Micro-controller
(2) IRC mode:
For some applications that do not require precise timing calculation, the RC oscillator could offer users with an
effective cost savings. eFTP5840 offer a versatile internal RC mode with default frequency value of 4M and
2MHz. In this mode, PLLC, XIN, XOUT and /RESET pins can defined to general purpose IO. The IRC
frequency will drift with the variation of voltage, temperature and process:
The frequency deviation of IRC mode:
Freq range (before adjust IR0~IR3)
Internal RC
Freq range (after adjust IR0~IR3)
(IR0~IR3 = 1111)
4M Hz
2M Hz
2.8M ~ 5.2M
1.4M ~ 2.6M
3.6M ~ 4.4M
1.8 M ~ 2.2M
*The frequency of IRC output can be adjust by setting IR0~IR3 in code option. By setting IR0~IR3, the
frequency deviation can be compensation. Please refer to code option to detail.
In IRC mode, PORT60, PORT61 and PORT70 are defined to bi-direction IO. By clearing P71S in code option
to 0, /RESET pin can also switch to INPUT pin (PORT71). In IRC mode, only two active modes can be
achieved, please refer to next figure to detail.
(3) ERIC mode:
ERIC mode is equipped with an internal capacitor and an external resistor (connected to VDD). The internal capacitor
functions as temperature compensator. In order to obtain more accurate frequency, a precise resistor is recommended.
Nevertheless, it should be noted that the frequency of the RC oscillator is influenced by the supply voltage, the
values of the even by the operation temperature. Moreover, the frequency also changes slightly from one chip to
another due to the manufacturing process variation. Besides, the package types, and the way the PCB is layout, have
certain effect on the system frequency. About the application is as below:
The frequency deviation of ERIC mode:
Internal C, external R
4M Hz (R=51K)
2M Hz(R=100K)
Freq range
3.5M ~ 4.4M
1.8M ~ 2.2M
VDD
R
ERIC
EM 78P5840
Fig 15: Application circuit of ERIC mode
ERIC’s oscillating frequency will base on IRC2’s CLK (determined on code option “IRC2S”). For example, if
IRC2S = 0, IRC2’s oscillating frequency is 2M Hz. At this time, by adjusting R, system CLK will be changed. But
the system CLK will always greater than 2M. That is to say, system CLK can only be adjusted between 2M to 6M.
Next two table show the corresponding between system oscillating CLK and the value of external resister.
The corresponding between system oscillating CLK and the value of external resister
Frequency (Hz)
External resister (ohm)
Operating Voltage (VDD)
3.0 ~5.5 V
6M
5M
4M
3.58M
2.1M
34K
41K
51K
57K
97K
2.8 ~5.5 V
2.5 ~5.5 V
2.2 ~5.5 V
2.2 ~5.5 V
*Only 2 types active mode (normal mode and sleep mode) are permitting in RC mode.
__________________________________________________________________________________________________________________________________________________________________
* This specification is subject to change without notice.
35
2004/11/10 V2.6
ELAN [ ELAN MICROELECTRONICS CORP ]
