at89c51snd1 ATMEL Corporation, at89c51snd1 Datasheet - Page 9

• Manufacturer Part Number: at89c51snd1
• Description: Mp3 Microcontrollers
• Manufacturer: ATMEL Corporation

Protocol
Overview
Communication Initialization
Autobaud Performances
Command Data Stream
Protocol
4241B–MP3–07/04
Table 5. Autobaud Performances
An initialization step must be performed after each Reset. After microcontroller reset,
the bootloader waits for an auto baud sequence (see Section “Autobaud Performances”,
page 9).
When the communication is initialized the protocol depends on the record type issued
by the host.
The host initiates the communication by sending a “U” character to help the bootloader
to compute the baud rate (auto baud).
Figure 4. Initialization
The bootloader supports a wide range of baud rates. 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. Table 5 shows the auto baud
capabilities.
Note:
All commands are sent using the same flow. Each frame sent by the host is echoed by
the bootloader.
Baudrate
9600
19200
38400
57600
115200
Communication Opened
Init Communication
Else
If (not received "U")
Time-out
1. Depending on the host, error values may lead to unsupported baudrate.
Host
AT89C51SND1 UART Bootloader
OK/KO
Status
OK
OK
OK
F
OSC
1
= 12 MHz
Error%
0.16
0.16
2.34
0.16
"U"
"U"
OK/KO
OK/KO
Status
OK
OK
OK
F
OSC
1
1
= 16 MHz
Error%
0.16
0.16
0.16
2.12
3.55
Sends Back ‘U’ Character
Performs Autobaud
Bootloader
Status
OK
OK
OK
OK
OK
F
OSC
= 20 MHz
Error%
0.16
1.36
1.36
1.36
0.16
9