Interfacing the MAX195 ADC to

Abstract: Application note for interfacing the MAX195 and MAX194 analog-to-digital converters (ADCs) to the TMS320C3X evaluation module. Example demo code is given. The demo software configures the TMS320C30 so that FSR1 and DR1 are inputs and CLKR1 and XF1 are outputs. To read the MAX194/MAX195, the software briefly drives the XF1 output low. The demo software polls the serial receiver until a complete frame has been received. Because this is just an interface demo, the software simply writes the received data word to the EVM host data port.

Overview

The MAX195 16-bit ADC can be interfaced to Texas Instruments' TMS320C30 DSP by means of its serial interface. The interface uses four wires plus ground. This application note explains how to interface the MAX194/MAX195 Evaluation Kit to the TMS320C3X Evaluation Module.

The example program was assembled using the TMS320C3X/4X COFF Assembler Version 4.50 and the TMS320C3X/4F COFF Linker Version 4.50 (copyright 1987 through 1992 by Texas Instruments Incorporated).

Interfacing the MAX194/MAX195 EVKIT to the TMS320C3X EVM

Maxim's MAX194/MAX195 Evaluation Kit can be interfaced to Texas Instruments' TMS320C3X Evaluation Module as follows:

1. Set the MAX194/MAX195 EVKIT jumpers according to Table 1.
2. Solder a 2-x-5-pin berg strip into MAX194/MAX195 EVKIT area J3. The PC board is already wired as shown in Table 2.
3. Connect a +5V power supply to the MAX194/MAX195 EVKIT.
4. Connect a 10-pin ribbon cable between the TMS320C3X EVM and the MAX194/MAX195 EVKIT.
5. Run the demo software.

Table 1. Jumper Settings

Jumper	Position	Function
JU1	Closed	Connects the MAX195 SCLK to ground
JU3	EXT	TMS320 CLKR1 drives the MAX195 conversion clock.
JU4	CS = GND	Connects the MAX195 Active-Low CS to ground
JU5	QSPI	TMS320 XF1 drives the MAX195 CONV.
JU6	Open	MAX195 reset/calibration command
JU7	UNI or OPEN	Selects unipolar or bipolar transfer function

Table 2. Ribbon-Cable Signals

Pin	MAX195	TMS320	Pin	MAX195	TMS320
1	DGND	GND	2	Active-Low EOC	FSR1
3	Not used		4	DOUT	DR1
5	Not used		6	Not used
7	Not used		8	Active-Low CONV	XF1
9	CONCLK	CLKR1	10	DGND	GND

How It Works

The demo software (see the program-code listing that follows) configures the TMS320C30 so that FSR1 and DR1 are inputs and CLKR1 and XF1 are outputs. The software uses the XF1 output to initiate a conversion. The XF1 pulse drives the MAX194/MAX195 conversion start input. The CLKR1 output provides the conversion clock to the MAX194/MAX195. Data output from the MAX194/MAX195 is received on the DR1 input. The FSR1 Frame Start signal is driven by the MAX194/MAX195 EOC (End of Conversion) signal, which marks the beginning of the serial frame.

To read the MAX194/MAX195, the software briefly drives the XF1 output low. The demo software polls the serial receiver until a complete frame has been received. Because this is just an interface demo, the software simply writes the received data word to the EVM host data port.

TMS320C3x/4x COFF Assembler, Version 4.50

Copyright (c) 1987-1992, Texas Instruments Incorporated

TMS320C30 Serial Port Initialization
Project: MAX195 EVKIT Interface to TMS320C3X EVM
Project file = MAX195I

Filename = MAX195I.ASM
Command file = MAX195I.CMD

Compile with the following commands:

   asm30 MAX195I -l
   lnk30 MAX195I.CMD

Pin Assignments:



Note: jumper JU8 must be OPEN
and CS must be tied to GND

Timing Diagram:



Fastest Clock 1MHz = (1 / 1000 nsec)
Minimum Receiver Timer Period = 4H

Receive Timer Period = 4 = 0.9375MHz
(System clock frequency = 30MHz)

Word diagram:

 .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 

Figure 1. Schematic.


Figure 2. Timing