SPI Interface User Manual for the MAX1441 Automotive, Two-Channel Proximity and Touch Sensor


This user manual describes how to use interface firmware to facilitateevaluation of the MAX1441 automotive, two-channel proximity and touchsensor during product development. The document assumes that the user is familiar with operating the MAX1441 and MAX1441EVSYS. It also assumes the user is familiar with the MAX-IDE or similar tools to upload an application firmware into the MAX1441 flash memory. For more information and detailed specification of the MAX1441 proximity and touch sensor, refer to the MAX1441 data sheet. For instructions on how to operate the MAX1441EVSYS and upload application firmware into the MAX1441 flash memory using the MAX-IDE application, consult the MAX1441EVSYS data sheet.

The MAX1441 SPI interface firmware is a standalone firmware that includes an initialization section for programming startup values of the MAX1441 registers (including range, conversion rate, and excitation frequency). The firmware must be loaded into the MAX1441 through the USB/JTAG interface and is the only firmware residing in the flash memory that is executed by the embedded micro.
The CMAXQUSB+ command module controller board is used for the interface between the MAX1441 evaluation board (MAX1441EVSYS+) and your computer. The driver for the CMAXQUSB+ board can be downloaded from Maxim's website. Choose the USB driver that is appropriate for your system.
Figure 1 shows interconnections between different components of the setup. A second USB connection can be used instead of the power supply, to power the MAX1441 on the master board. The user interface program resides in the PC and facilitates communication between the user and the MAX1441 through a command-line window called MAX1441_Console. Communication rate between the MAX1441 and CMAXQUSB+ board is fixed at 31.25kHz.
Figure 1. Block diagram of hardware setup.
Figure 1. Block diagram of hardware setup.

Hardware Setup

  1. Verify that JU105 on the MAX1441 evaluation board is in position 2–3.
  2. Load the SPI Interface_Rxx firmware to the MAX1441 flash memory (using MAX-IDE or equivalent application).
  3. Remove jumpers JU120 through JU124.
  4. Connect the cable between the CMAXQUSB interface board and the MAX1441 evaluation board.
  5. Power the MAX1441 evaluation board (if not already powered) through an external supply or a USB port:
      a. If powering through a USB port, two USB cables are needed: one to power and communicate with the CMAXQUSB board and one to power the MAX1441.
      b. If powering through an external supply, move jumper JU4 to position 2–3 and apply external power to 6V < VBAT < 28V terminals.
  6. Connect a USB cable from the CMAXQUSB board to the PC.
  7. Execute the MAX1441_Console.exe application.
See Figure 3 for a drawing of the interface harness between the MAX1441EVSYS+ and CMAXQUSB+ interface boards.
Note: Jumpers JU120, JU121, JU122, JU123, and JU124 must be removed from the MAX1441 evaluation board before operating the SPI interface.

Using the MAX1441_Console Program

Once the SPI Interface firmware is written to the MAX1441 flash memory, and hardware is set up to communicate SPI, launch the MAX1441_Console.exe application. All modifications and inquiries of the MAX1441 internal registers status is achieved through a Read or a Write command. For a list of commands acceptable by the MAX1441_Console, see Table 1.
Table 1. MAX1441_Console Commands
Command Description Example Return
Init System will search the USB ports with CMAXQUSB board connected Init CMD: init
Found or Not Found message
logfile on Will create and opens a log file "MAX1441log.txt"
(If file already exists, it will be cleared)
logfile on CMD: logfile on
logfile off Will close the MAX1441log.txt file logfile off CMD: logfile off
delay value Will cause a delay of value between each CS-cycle (value is in seconds) Delay 3 CMD: delay 3
w address value Write value to the register specified by address. Value is always in hexadecimal format w 3 22 CMD: w 3 22
r address #ofData #ofCS-cycles Read #ofData times for each #ofCS-cycles from register at address r 0 2 3 CMD: r 0 2 3
To write to an internal register, a Write command "w" must be issued. To read an internal register a Read command, "r" must be issued. Upper or lower case letters are valid for read and write commands. Any command other than the ones listed on the table above will result in an error message on the MAX1441_Console window and no action will be taken. For every Read or Write command from the MAX1441_Console to the CMAXQUSB board, a Chip Select (CS) line low/high cycle will be issued to the MAX1441EVSYS board. Duration of CS cycle is based on the number of data points requested.
Figure 2. MAX1441_Console window.
Figure 2. MAX1441_Console window.

Write Command

A Write command has a w Address Value format, where Address is the assigned register value given in Table 1 and Value is the value to be written to the register specified by Address. For example, command w 5 2 will write "2" to CO1 register. Value is always in hexadecimal format.

Read Command

A Read command has the r Address #ofData #ofCS-cycles format, where, Address is address of the register to read; #ofData is number of readings from the register specified by Address during one CS cycle; and #ofCS-cycles is how many times CS line will cycle.
Maximum of 62 16-bit readings can be made from the MAX1441 during one CS- cycle. Each 16-bit reading will take approximate 600µs. A maximum of 1000 CS-cycle can be specified in a one command. The parameters #ofData and #ofCS-cycles apply to all registers; however, they are mostly relevant to CRSLT1H, CRSLT1L, CRSLT2H, and CRSLT2L registers. The delay command can extend monitoring of the MAX1441 performance for longer period of time. A delay of value seconds, specified in the delay command, will be applied after each CS-cycle. The format of response to a Read command is Time, data#, cycle#, Data, where Time is number of seconds elapsed since start of test, data# is the counter associated with #ofData, and cycle# is the counter associated with the #ofCS-cycle. Table 2 lists registers and the associated addresses that can be written/read using the MAX1441_Console application. Consult the MAX1441 data sheet for detailed definition and function of each register.
Table 2. Register Addresses in Read and Write Commands
Address Register Affected By Write Command Register(s) Content Reported in Response to Read Command Description
High Byte Low Byte
0 CRSLT2H CRSLT1H Channel 2 and Channel 1 conversion results (4 LSBs and Overflow bits not reported)
1 CRSLT1H CRSLT1L Channel 1 conversion results
2 CRSLT2H CRSLT2L Channel 2 conversion results
3 CRNG 0x00 CRNG Input capacitance range
4 FEL 0x00 FEL Excitation Frequency
5 FEB 0x00 FEB Bandwidth of the spread spectrum modulation
6 DSB 0x00 DSB Standby conversion rate
7 SSB2 0x00 SSB2 Channel 2 standby conversion rate subdivider
8 CO1 0x00 CO1 Channel 1 capacitance offset
9 CO2 0x00 CO2 Channel 2 capacitance offset
10 AT1H 0x00 AT1H Channel 1 absolute threshold
11 AT2H 0x00 AT2H Channel 2 absolute threshold
12 RT1H 0x00 RT1H Channel 1 rate of change threshold
13 RT2H 0x00 RT2H Channel 2 rate of change threshold
14 PD 0x00 PD Power-Down Register
15 SCT 0x00 SCT Single Conversion Register
16 AFEINRST 0x00 AFEINRST AFE Interrupt Status Register
17 WU1 0x00 WU1 Channel 1 Wake-Up Control Register
18 WU2 0x00 WU2 Channel 2 Wake-Up Control Register
(Note 1)
(Note 2)
0x?? 0x?? Unrecognized address; address will be returned by the MAX1441
  1. "??" denotes any invalid address. Valid addresses can be in decimal or hexadecimal format.
  2. The command returns previous value in response to any invalid address, for example "ab". 0xab is a valid address and 0xABAB will be returned.

Storing Data to a File

All communications over the interface can be stored into a log file in .txt format. Storing of data into a file is started by issuing the logfile on command. Logging data can be stopped by issuing the logfile off command. The log file created is named "MAX1441.txt" and it will be cleared every time command logfile on is issued. As an example, content of a log file for command r 0 3 4 is shown in Figure 3. To avoid overwriting a log file with useful data, rename the log file before new logfile on command is issued.
Figure 3. Example of log file content.
Figure 3. Example of log file content.
Figure 4. Interface harness between the MAX1441EVKIT and the CMAXQUSB board.
Figure 4. Interface harness between the MAX1441EVKIT and the CMAXQUSB board.



Youssof Fathi