More Design Topics

Serial Port Baud Rate

The baud rate of serial port is generated by a 16-bit prescaler which uses an internal clock source at 937,500 Hz. (15 MHz / 16). Most speeds between 300 bps to 230400 bps can be generated with minor errors.

Baud Rate	Actual	Error %
300 bps	300 bps	0.00
600 bps	600 bps	0.00
1,200 bps	1,200 bps	0.00
2,400 bps	2,403 bps	0.12
4,800 bps	4,807 bps	0.15
9,600 bps	9,664 bps	0.67
19,200 bps	19,531 bps	1.72
38,400 bps	39,062 bps	1.72
57,600 bps	58,593 bps	1.72
76,800 bps	78,125 bps	1.73
115,200 bps	117,187 bps	1.72
230,400 bps	234,375 bps	1.73

Stack Size

The stack size for applications is fixed at 4 KB. When using auto variables, special care should be taken for ensuring not to exceed this limit. To avoid possible problems with stack overflow, using auto variables should be more conservative:

Not recommended

int function()

{ char buf[1024]; // in stack

…..

}

Ok

int function()

{ char *buf;

buf=(char *)malloc(1024); // use heap memory

…..

free(buf);

}

CGI Timeout

The timeout of CGI has been set to 300 seconds (5 minutes). When operating over Internet, web-based firmware updating may exceed this timeout limit. Therefore, it is not recommended to upgrade firmware over Internet which could make your device unusable.