MAX195和MAX194模數(shù)轉(zhuǎn)換器（ADC）與TMS320C3X評(píng)估模塊接口的應(yīng)用筆記。給出了示例演示代碼。演示軟件配置 TMS320C30，使 FSR1 和 DR1 為輸入，CLKR1 和 XF1 為輸出。為了讀取MAX194/MAX195，軟件將XF1輸出短暫驅(qū)動(dòng)為低電平。演示軟件輪詢串行接收器，直到收到完整的幀。由于這只是一個(gè)接口演示，軟件只需將接收到的數(shù)據(jù)字寫入 EVM 主機(jī)數(shù)據(jù)端口即可。

概述

MAX195 16位ADC可通過串行接口連接至德州儀器TMS320C30 DSP。該接口使用四根電線加接地。本應(yīng)用筆記說明如何將MAX194/MAX195評(píng)估板連接至TMS320C3X評(píng)估模塊。

示例程序是使用 TMS320C3X/4X COFF 匯編程序版本 4.50 和 TMS320C3X/4F COFF 鏈接器版本 4.50（1987 年至 1992 年版權(quán)歸德州儀器公司所有）組裝的。

MAX194/MAX195評(píng)估板與TMS320C3X EVM接口

Maxim的MAX194/MAX195評(píng)估板可與德州儀器TMS320C3X評(píng)估模塊接口，如下所示：

根據(jù)表1設(shè)置MAX194/MAX195評(píng)估板跳線。

將2 x-5引腳伯格條焊接到MAX194/MAX195評(píng)估板J3區(qū)域。這 PC 板已接線，如表 2 所示。

將+5V電源連接至MAX194/MAX195評(píng)估板。

連接 TMS320C3X EVM 和 MAX194/MAX195 之間的 10 針帶狀電纜 評(píng)估板。

運(yùn)行演示軟件。

工作原理

演示軟件（請(qǐng)參閱下面的程序代碼列表）配置 TMS320C30，以便 FSR1 和 DR1 為輸入，CLKR1 和 XF1 為輸出。該軟件使用 XF1 輸出來啟動(dòng)轉(zhuǎn)換。XF1脈沖驅(qū)動(dòng)MAX194/MAX195轉(zhuǎn)換啟動(dòng)輸入。CLKR1輸出為MAX194/MAX195提供轉(zhuǎn)換時(shí)鐘。MAX194/MAX195的數(shù)據(jù)輸出由DR1輸入端接收。FSR1幀啟動(dòng)信號(hào)由MAX194/MAX195 EOC（轉(zhuǎn)換結(jié)束）信號(hào)驅(qū)動(dòng)，該信號(hào)標(biāo)志著串行幀的開始。

為了讀取MAX194/MAX195，軟件將XF1輸出短暫驅(qū)動(dòng)為低電平。演示軟件輪詢串行接收器，直到收到完整的幀。由于這只是一個(gè)接口演示，軟件只需將接收到的數(shù)據(jù)字寫入 EVM 主機(jī)數(shù)據(jù)端口即可。

TMS320C3x/4x COFF 匯編程序，版本 4.50

版權(quán)所有 （c） 1987-1992，德州儀器公司

TMS320C30 串行端口初始化
項(xiàng)目：MAX195 評(píng)估板與 TMS320C3X EVM
項(xiàng)目文件接口 = MAX195I

文件名 = MAX195I。ASM
命令文件 = MAX195I。CMD

使用以下命令進(jìn)行編譯：

asm30 MAX195I -l
lnk30 MAX195I.CMD

引腳分配：

注意：跳線 JU8 必須打開
，CS 必須連接到 GND

時(shí)序圖：

最快時(shí)鐘 1MHz = （1 / 1000 nsec）
最小接收器定時(shí)器周期 = 4H

接收計(jì)時(shí)器周期 = 4 = 0.9375MHz
（系統(tǒng)時(shí)鐘頻率 = 30MHz）

字圖：

 .sect    "vectors" 
 reset .word  init 
 int0 .word  init 
 int1 .word  init 
 int2 .word  init 
 int3  .word  init 
 xint0 .word  init 
 rint0  .word  init 
 xint1 .word  init 
 rint1  .word  init 
 tint0 .word  init 
 tint1  .word  init 
 dint .word  init 
 
   .data       
    STCK  .word  0809F00H ; initial stack pointer 
           
    CTRL .word  0808000H ; peripheral interface base address 
    HOST_DATA  .word  0804000H ; host data port address 
              
    IOF_AMASK  .set  0000EH ; clear all XF1 bits in IOF register 
 IOF_SET_XF1  .set  00060H ; make XF1 pin an output; value = 1 
 IOF_RESET_XF1  .set  00020H ; make XF1 pin an output; value = 0 
 IOF_INPUT_XF1  .set  00080H ; make XF1 pin an input; read its value 
           
 FS_AMASK  .set  0F0FFH ; mask for an FS pin 
 SET_FS  .set  00600H ; make FS a high output 
 RESET_FS  .set  00200H ; make FS a low output 
 GET_FS  .set  00800H ; input mask for FS pin 
           
 D_AMASK  .set  0FF0FH ; mask for a Data pin 
 SET_D  .set  00060H ; make D a high output 
 RESET_D  .set  00020H ; make D a low output 
 GET_D  .set  00080H ; input mask for D pin 
           
 CLK_AMASK  .set  0FFF0H ; mask for a CLK pin 
 SET_CLK  .set  00006H ; make CLK a high output 
 RESET_CLK  .set  00002H ; make CLK a low output 
 GET_CLK  .set  00008H ; input mask for CLK pin 
 
   Serial Port Global Control Register
 
 SerGlob1  .word 08100280H
 
 08000000H:  RRESET - reset / enable the receiver 
 0080H:  RCLKSRCE - use internal receive clock (CLKR pin is an output) 
 0200H: 
  RVAREN - Receiver Variable Data Rate 
 00100000H:  RLEN = 2 bytes (16 bits) 
 
   Pin Assignment Register for FSX, CLKX, DX
 
 SerPrtX1   .word 00H
 
   assign CLKX pin to general I/O 
   make CLKX an input 
   assign DX pin to general I/O 
   make DX an input 
   assign FSX pin to general I/O 
   make FSX an input 
 
   Pin Assignment Register for FSR, CLKR, DR
 
 SerPrtR1   .word 0111H
 
 
 0001H:  assign CLKR pin to serial port clock 
 0010H:  assign DR pin to serial port receive data 
 0100H:  assign FSR pin to serial port frame start 
 
   Serial Port Timer Global Control Register
 
 SerTim1  .word 03C0H
 
 
  XHLD 0=hold transmit timer 
  XC/P  0=pulse mode 
  XCLKSRC 0=CLKX pin increments the counter 
 0040H:  RGO=1 --  start the receive timer 
 0080H:  RHLD 1=run receive timer 
 0100H:  RC/P  1=clock (50% duty cycle) 
 0200H:  RCLKSRC  1=use 7.5MHz time base (30MHz system clock/4) 
 
   Serial Port Timer Period Register
 
 SerTim1Val   .word 040000H
 
 
 0 H:  Transmit Counter Period 
 4 H:  Receive Counter Period 
 
   Receive Timer Period = 4 = 0.9375MHz
 
     .text
 init 
 
 
 LDI  0,ST  ; initialize status register 
 LDI  0,DP  ; point data page pointer into rom 
 LDI  @STCK,SP  ; initialize stack pointer 
 
   ; start with XF1 high
   ; 
 
 
 LDI  IOF,R1  ; get XF1 settings 
 AND  IOF_AMASK,R1  ; don't touch XF0 settings 
 OR  IOF_SET_XF1,R1  ; make XF1 output a high value 
 LDI  R1,IOF  ; write new XF1 settings 
 
   ; initialize serial port
   ; 
 
 
 LDI  @CTRL,AR0  ; peripheral interface address 
 LDI  @HOST_DATA,AR1  ; host interface address 
        
 LDI  @SerTim1Val,R0     
 STI  R0,*+AR0(86)  ; serial ch1 timer period 
        
 LDI  @SerGlob1,R0     
 STI  R0,*+AR0(80)  ; serial global register 
        
 LDI  @SerPrtX1,R0     
 STI  R0,*+AR0(82)  ; serial transmit control register 
        
 LDI  @SerPrtR1,R0     
 STI  R0,*+AR0(83)  ; serial receive control register 
        
 LDI  @SerTim1,R0     
 STI  R0,*+AR0(84)  ; serial ch1 timer register 
 
 XF1 signal is named Active-Low CONV to MAX195 EVKIT
 
 This is how we set XF1:
 
 
 LDI  IOF,R1  ; get XF1 settings 
 AND  IOF_AMASK,R1  ; don't touch XF0 settings 
 OR  IOF_SET_XF1,R1  ; make XF1 output a high value 
 LDI  R1,IOF  ; write new XF1 settings 
 
 This is how we clear XF1:
 
 LDI  IOF,R1  ; get XF1 settings 
 AND  IOF_AMASK,R1  ; don't touch XF0 settings 
 OR  IOF_RESET_XF1,R1  ; make XF1 output a low value 
 LDI  R1,IOF  ; write new XF1 settings 
 
 next_sample:
 
   generate conversion start pulse
 
 
 LDI IOF,R1  ; get XF1 settings 
 AND IOF_AMASK,R1  ; don't touch XF0 settings 
 OR IOF_RESET_XF1,R1  ; make XF1 output a low value 
 LDI R1,IOF  ; write new XF1 settings 
 AND IOF_AMASK,R1  ; don't touch XF0 settings 
 OR  IOF_SET_XF1,R1  ; make XF1 output a high value 
 LDI R1,IOF  ; write new XF1 settings 
 
   wait until serial receive is complete
 
 loop
 
 
 LDI *+AR0(80),R2  ; read global control register 
 AND 01H,R2  ; test the receiver ready bit 
 BZ loop  ; loop until data is received 
 
   get the received data
 
 LDI *+AR0(92),R3  ; copy received data into R3 
 
 this demo application does no processing --
 it just makes the value available to the
 TMS320C3X EVM's host.
 
 STI R3,*+AR1(0) ; send R3 to host 
 
 LDI  100,R0  ; delay 
 
 wait_loop:
 
 
 SUBI 1,R0 
 BNZ  wait_loop 
 
 BR  @next_sample  ; this program runs forever 
 
 .end 

圖1.圖解的。

圖2.定時(shí)。

審核編輯：郭婷