Interface Design between 80C32E MCU and TLV2548 Serial A/D

O Introduction

TLV2548 is a 12-bit, multi-channel, small size, low power consumption, high-speed serial A/D conversion chip produced by TI. It has a frame synchronization (FS) signal specifically connected to DSP, so it can be widely used in DSP high-speed data acquisition systems.

The MCS-51 series of microcontrollers have gone through many years of development, and their application technology has become very stable and reliable. TLV2548 is small in size and has a simple interface. Both chips have had experience in space flight, so they can be used in aerospace products with low cost, simple control, small data processing volume, and high reliability requirements.

Therefore, this paper will introduce the design method of the interface circuit and control program of 80C32E microcontroller and TLV2548.

1 Interface circuit design

The interface circuit between 80C32E and TLV2548 is shown in Figure 1.

The TLV2548 provides an SPI serial port. The 80C32E uses a general-purpose I/O port (P1) and generates SPI serial interface signals through software programming to control the TLV2548 and read and write data.

TLV2548 has 5 control pins , FS, SCLK, and . FS is a DSP-specific frame synchronization signal. When in microcontroller control mode, it can be connected to a high level; when it is low, the analog circuit and reference circuit in the chip enter a power-saving state. Since this article does not use the power-saving mode, it is connected to a high level. In addition, the pin is a signal for the end of conversion and requesting an interrupt to the processor . The falling edge of indicates that the converted data can be output. In this circuit, this signal is not connected because the conversion speed of TLV2548 is very fast (3.6μs), and the microcontroller interrupt and search method cannot improve the time efficiency. Therefore, software delay is used to wait for the conversion to end. This is relatively simple to program and can also save the hardware resources of 80C32E. The data lines SDI and SDO are the data transmission lines between 80C32E and TLV2548.
TLV2548 has four conversion modes: single (00), repeat (01), scan (10) and repeat scan (11). The usage of each mode is slightly different; there are two sampling modes: normal and extended. The advantage of the extended sampling method is that the sampling and conversion time of A/D is not limited by the clock signal SCLK, and its sampling and conversion are controlled by the level. The time is short and the speed is fast. This paper selects the 11-repeat scanning mode and the extended sampling method to convert the 6 channels (A0~A5) in TLV2548.

The MAX706 in Figure 1 is the watchdog reset circuit, and OSCIC is a 16 MHz crystal oscillator.

2 Control Program Design

The data and commands between 80C32E and TLV2548 are transmitted in 16-bit binary format. The command format is: high 4-bit command + low 12-bit configuration word. The configuration register (CFR) readout format is: high 4-bit ignore + low 12-bit register content. The A/D conversion value (FIFO) readout format is: high 12-bit conversion value + low 4-bit ignore.

The task of the 80C32E interface control program is to generate A/D sampling and conversion signals, as well as SPI serial port timing, and complete the conversion start of TLV2548, conversion mode setting and conversion result value reading. The program flow is shown in Figure 2.

The interface control program of TLV2548 is introduced below in conjunction with Figure 1 and Figure 2.

The first is initialization, that is, after power-on, 80C32E configures TLV2548. When configuring, first set SCLK (P1.3) to low level. Secondly, set low (P1.6) to make the signal produce a falling edge. At this time, since FS is high level. In this way, when the falling edge of comes, TLV2548 defaults to the microcontroller (μP) system, which will reset the internal counter and enable SDI and SD-O. Finally, 80C32E writes the command word A000H to TLV2548 (CFR), thereby completing the initialization of TLV2548. The program code is:

When configuring. You can choose the TLV2548 external reference voltage and internal oscillator, and select mode 11 repeated scan mode, the scan sequence is 0-1-2-3-4-5, and the scan sequence length is 3/4. The specific code is:

3 Experimental results
When 80C32 successfully performs initialization configuration, it can send 6 pulses to TLV2548 by clearing and setting to start A/D sampling and conversion. The falling edge of A/D output indicates that the conversion is completed and the result data can be output. The subsequent falling edge will make the signal high, select TLV2548 and make SDI and SDO valid. Finally, 80C32 sends out the serial clock signal SCLK (P1.3) and shifts out commands and reads in data through SDI and SDO. Figure 3 shows the TLV2548 control timing diagram after running the above program.

4 Conclusion

At present, the scheme has been applied to a certain space mission. Practice has proved that the system has good performance and has passed the electrical, identification, and sample acceptance. In view of the compatibility of the microcontroller, the interface circuit and program introduced in this article can also be applied to other models of MCS-51 series microcontrollers.