Datasheet

8
4266C–CAN–03/08
AT89C51CC03 UART Bootloader
Protocol
Overview An initialization step must be performed after each Reset. After microcontroller reset, the boot-
loader waits for an autobaud sequence (see Section “Autobaud Performances”).
When the communication is initialized the protocol depends on the record type issued by the
host.
Communication
Initialization
The host initiates the communication by sending a ’U’ character to help the bootloader to com-
pute the baud rate (autobaud).
Figure 2. Initialization
Autobaud
Performances
The bootloader supports a wide range of baud rates. It is also adaptable to a wide range of oscil-
lator frequencies. This is accomplished by measuring the bit-time of a single bit in a received
character. This information is then used to program the baud rate in terms of timer counts based
on the oscillator frequency. Table 2 shows the autobaud capabilities.
Host
Bootloader
"U"
Performs Autobaud
Init Communication
If (not received "U")
"U"
Communication Opened
Else
Sends Back ‘U’ Character
Table 2. Autobaud Performances
Frequency
(MHz)
Baudrate
(kHz) 1.8432 2 2.4576 3 3.6864 4 5 6 7.3728
2400 OK OK OK OK OK OK OK OK OK
4800 OK - OK OK OK OK OK OK OK
9600 OK - OK OK OK OK OK OK OK
19200 OK - OK OK OK - - OK OK
38400 - - OK OK - OK OK OK
57600 - - - - OK - - - OK
115200 - - - - - - - - OK
Frequency
(MHz)
Baudrate
(kHz) 8 10 11.0592 12 14.746 16 20 24 26.6
2400 OK OK OK OK OK OK OK OK OK
4800 OK OK OK OK OK OK OK OK OK
9600 OK OK OK OK OK OK OK OK OK
19200 OK OK OK OK OK OK OK OK OK