EM78P803B

8-bit Micro-controller

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2006/2/27

V1.3.5

VII.13 ERIC Mode

The system has an optional RC mode. In this ERIC mode, user can connect PLLC to VDD with a resistor serially.

Then the system will generate a clock signal internally by an internal capacitor and external resistor on PLLC pin.

User can use only one resistor to replace the crystal oscillator in order to reduce PCB area and cost.

In ERIC mode, the main frequency is provided by ERIC oscillation and the sub frequency is provided by the

main frequency through the scaler. User can configure the scaler with different factors in order to get the suitable

match with peripheral of system (like LCD driver, R to F counter or 16-bit counter) and main frequency. For

example, for low power application with LCD display, user can choose the frequency 1MHz with scale factor 32.

The sub frequency will be about 32kHz. With this frequency, the LCD panel can work well.

In the other hand, user can choose a suitable sub frequency which is different from 32kHz (For example, high

frequency LCD panel). Then choose the right Main frequency and set the scale factor correctly. But be careful,

the sub frequency you choose cannot let the other function work well. User can refer following table to get

32kHz sub frequency.

The formula of ERIC frequency is f=1/(Rx5.25x10

about 1.9MHz.The following table shows the suggested resistor and approximate main frequency. The scaler

doesn’t work when in crystal mode. In crystal mode, the sub frequency is always 32kHz. The following tables

shows the suggested serial connected resistor and generated main frequency, scale factor and sub frequency.

Ext. Resistor

RC Frequency

Scale Factor

Sub. Frequency

1.5M

127k

4

31.8k

750k

254k

8

31.8k

360k

529k

16

33.1k

180k

1059k

32

33.1k

91k

2110k

64

33k

47k

4054k

128

31.7k

22k

8662k

256

33.8k

In ERIC mode, the main and sub frequency act at the same time. Thus, the operating modes of system are only

normal mode and sleep mode.

The frequency of ERIC oscillator affected by operating voltage. The higher operating voltage the MCU has, the

faster frequency the ERIC oscillator generates. According to our laboratory test, the following table shows the

highest frequency in different operating voltage. Notice that it is our laboratory measured data. It is probably

different in practical situation. And it will vary from different EM78801s. The resistance shows in the table

might not be suitable for the formula of ERIC oscillation mentioned before. The formula has a bit changed

because the frequency is too fast.

Power

ERIC Oscillation

Serial Resistance

1

2.2V

6.84MHz

30.13k

2

2.6V

9.96MHz

20.29k

3

3V

11.63MHz

18.4k

4

4V

15.11MHz

13.98k

5

5V

18.12MHz

11.75k

6

5.5V

19.27MHz

11.02k