AT89C51AC2(2005) データシートの表示（PDF） - Atmel Corporation
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AT89C51AC2 Datasheet PDF : 29 Pages
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A/T89C51AC2 UART Bootloader
Protocol
Overview
An initialization step must be performed after each Reset. After microcontroller reset,
the bootloader 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 compute the baudrate (autobaud).
Figure 4. Initialization
Host
Bootloader
Init Communication
’U’
Performs Autobaud
If (not received ’U’)
Else
Communication Opened
Sends Back ‘U’ Character
’U’
Autobaud Performances
4231C–CAN–03/05
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 2 shows the autobaud capabilities.
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
9600
19200
OK
-
OK
OK
OK
OK
OK
OK
OK
OK
-
OK
OK
OK
OK
OK
OK
OK
OK
-
OK
OK
OK
-
-
OK
OK
38400
57600
-
-
OK
OK
-
OK
OK
OK
-
-
-
-
OK
-
-
-
OK
115200
-
-
-
-
-
-
-
-
OK
Frequency
(MHz)
Baudrate
(kHz)
8
11.059
10
2
12 14.746 16
20
24
26.6
2400
OK
OK
OK
OK
OK
OK
OK
OK
OK
4800
9600
OK
OK
OK
OK
OK
OK
OK
OK
OK
OK
OK
OK
OK
OK
OK
OK
OK
OK
19200
OK
OK
OK
OK
OK
OK
OK
OK
OK
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