Datasheet

104
4235K–8051–05/08
AT89C51RD2/ED2
• SBV = FCh
• SSB = FFh
The Full Chip Erase does not affect the bootloader.
24.8.3 Checksum Error
When a checksum error is detected, send ‘X’ followed with CR&LF.
24.9 Flow Description
24.9.1 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 requested by the
host.
FLIP, a software utility to implement ISP programming with a PC, is available from the Atmel
web site.
24.9.2 Communication Initialization
The host initializes the communication by sending a ’U’ character to help the bootloader to com-
pute the baudrate (autobaud).
Figure 24-7. Initialization
24.9.3 Autobaud Performances
The ISP feature allows a wide range of baud rates in the user application. It is also adaptable to
a wide range of oscillator 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. The ISP feature requires that an initial character
(an uppercase U) be sent to the AT89C51RD2/ED2 to establish the baud rate. Table show the
autobaud capability.
Host
Bootloader
"U"
Performs Autobaud
Init Communication
If (Not Received "U")
"U"
Communication Opened
Else
Sends Back “U” Character
Table 24-8. 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