Toshiba??USIO21

USIO21一般由控制電路、運(yùn)算器和寄存器組成，這些電路一般都集成在一個(gè)芯片上。CPU通過地址總線、數(shù)據(jù)總線和控制總線與存儲(chǔ)單元。輸入輸出（I/O）接口電路相連接。

? ? USIO21它主要完成以下的功能：

（1）將輸入信號(hào)送入PLC中存儲(chǔ)起來。??

（2）按存放的先后順序取出? ? ? ? ? ? ?

用戶指令，進(jìn)行編譯。? ? ? ? ? ? ? ? ??

（3）完成用戶指令規(guī)定的各種操作。? ? ? ?

（4）將結(jié)果送到輸出端。

（5）響應(yīng)各種外圍設(shè)備（如變程器、打印機(jī)等）的請(qǐng)求。

? ? 2、存儲(chǔ)器

USIO21內(nèi)部存儲(chǔ)器有兩類：一類是RAM（即隨機(jī)存取存儲(chǔ)器），可以隨時(shí)由 CPU對(duì)它進(jìn)行讀出、寫入；另一類是ROM （即只讀存儲(chǔ)器），CPU只

從中讀取而不能寫入。RAM主要用來存放各種暫存的數(shù)據(jù)、中間結(jié)果能及用戶正在調(diào)試的程序，ROM主要存放監(jiān)控程序及用戶已調(diào)試好的程序，這些程序都事先燒在ROM芯片中，開機(jī)后便可運(yùn)行其中程序。

Central processing unit (CPU) is generally composed of control circuit, arithmetic unit and register. These circuits are generally integrated on one chip. CPU is connected with storage unit and b / output (I / O) interface circuit through address bus, data bus and control bus.There are two types of PLC internal memory: one is RAM (random access memory), which can be read and written by CPU at any time; the other is ROM (read only memory), which is only used by USIO21

Read from but not write to. Ram is mainly used to store various temporary data, USIO21 intermediate results and programs being debugged by users. ROM is mainly used to store monitoring programs and programs debugged by users. These programs are burned in ROM chip in advance, and the programs can be run after startup.