兩種器件系列的代碼略有不同，但是功能本質是一樣的。該目標實現的壓力在于爭取最大的性能和功能, 同時要求最少的代碼空間。

FIRMWARE Basic Operation（固件基礎操作）

圖1  BootLoader 功能塊圖

Figure 1 summarizes （總結）the essential firmware design of the bootloader. 

圖1總結了bootloader的基本固件設計。

Data is received through the USART module, configured in Asynchronous mode for compatibility（兼容性） 

with  RS-232 and passed through the transmit/receive engine. 

數據通過USART（串口）模塊接收，配置為異步模式，通過發送/接收引擎下載，比如RS232。

The engine filters and parses the data, storing the information into a data buffer in RAM. 

引擎過濾并解析數據, 然后存儲信息到在RAM的數據緩沖區中。

The command interpreter evaluates the command information within the buffer to determine what
should be done (i.e., Is the data written into a memory unit? Is data read from a memory unit? 

Does the firmware version need to be read?). 

命令解釋器評估在緩沖區的命令信息來確定應該做什么。（比如：該數據是在存儲單元以寫進去的，

還是數據從該存儲單元讀取？固件版本是否需要讀取？）

Once the operation is performed, data is passed back to the transmit/receive engine to be transmitted 

back to the source, closing the software flow control loop.

一旦操作方式被確定，被傳遞到發送/接收引擎的數據會被返送到宿主機，并關閉軟件流控制回路。

COMMUNICATIONS （通信）
The microcontroller’s USART module is used to receive and transmit data; it is configured as a UART to
be compatible with RS-232 communications. 
微控制器的USART模塊被用于接收和傳送數據，它被確定用于UART去兼容與RS-232的通信。
The device can be set up in an application to bootload from a computer through its standard serial interface.
該器件能夠通過它的標準串口從電腦引導加載建立起一個應用程序。
The following communications settings are used:
? 8 data bits
? No parity
? 1 STOP bit
下列通信設置將會被用到：
? 8個數據位
? 無校驗位
? 1個停止位

The baud rate setting is variable depending on the application. Baud rate selection is discussed later.

波特率設置根據應用程序是可變的。波特率的選擇稍后討論。

THE RECEIVE/TRANSMIT BUFFER（ 接收和傳送緩沖區）
All data is moved through a buffer (referred to as the Receive/Transmit Buffer). 　　
所有的數據都是通過一個緩沖區移動(稱為接收/發送緩沖區)。
The buffer is a maximum of 255 bytes deep. 
緩沖區大小的最大值為255字節。
This is the maximum packet length supported by the protocol.
這個最大包長度有被協議支持。
 However, some devices may not support the largest packet size due to memory limitations. 
但是，一些器件由于內存大小并不支持該最大包長度。

Note: The actual packet length supported by a particular device depends on the size of its data memory.
注:  實際的包長度所支持的 特定器件取決于它的數據存儲區的大小。

Figure 2 shows an example of the mapping of the buffer within the PIC18F452.
圖2 顯示了一個示例關于PIC18F452內的緩沖區映射。

圖2 數據內存在PIC18F452的利用

A useful feature of the receive/transmit buffer is that it retains its memory between packets, thus 

allowing very fast repeat and replication operations. That is, if an empty packet is sent, the data