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.

OverviewThe 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 EVMMaxim'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 WorksThe 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:

Figure 1. Schematic.


Figure 2. Timing