Based on NXP S32K144 & NJJ29C2 PEPS keyless entry solution

The keyless entry and start system of the car is referred to as the PEPS (Passive Entry Passive Start) system, which consists of a controller, a radio frequency (RF) transmitter in the smart key, and a receiver on the car side. When the key is within the effective range, the owner pulls the car door or presses a key to start the switch, the corresponding module will send a terminal signal to wake up the main controller and start the entire communication process. The whole process does not require the use of a key to open the car door or start the engine. The PEPS system brings convenience and comfort to the owner (intelligent access control, keyless entry/start), and more importantly, it greatly improves safety.

Shiping Group has launched a keyless entry solution for automobiles based on NXP S32K144 (base station master control), NXP NJJ29C2 (low frequency drive), NXP NCF29A1 (key), and NXP NCK2912 (ultra-high frequency reception). The solution can realize car key ID storage, car keyless entry (PKE), no keyless entry (PKE), no keyless entry (PKE), no keyless entry (PKE), no keyless entry (PKE), no keyless entry (PKE), no keyless entry (PKE), no keyless entry (PKE), no keyless entry (PKE), no keyless entry (PKE), no keyless entry (PKE),Car key activation (PKG), car anti-theft (IMMO), remote control (RKE) and other functions. The focus of this program is to switch and update the hardware platform, switch the MCU to S32K144, and replace the low-frequency transmitter module with NJJ29C2. Differences in hardware have also led to differences in software writing. Overall, since NJJ29C2 has added optional IRQ and BUSY lines to the SPI link, this makes the transmission timing requirements of NJJ29C2 commands no longer as stringent as before (only need to monitor IRQ and BUSY). At the same time, the effect of this program is presented on children's cars, which makes the functional scenario more intuitive.

 

1. Antenna layout：

NJJ29C2 has a total of 9 sets of antennas that can be used, but due to the limitations of children's car space and the lack of trunk and other conditions, only 4 sets of antennas are currently used, the relative position is shown in Figure 1. The renderings of the trolley after the actual assembly are shown in Figure 2.

1) TX1 + TX2, using high-power drive mode (the maximum current can be increased to 2.5 A), located in the center of the car, send PKE/PKG RSSI measurement command (the RSSI threshold value in the software is adjusted according to the child car, not according to the actual vehicle environment, it needs to be adjusted according to the actual situation), Detect the relative position of the key.

2) TX3, located at the car door handle, is used for PKE HT-3 certification.

3) TX6, located near the driver's seat, is PKG HT-3 certified.

4) TX9/RX1, located inside the center console, under the one-key start button, to ensure that the engine can still be started by IMMO when the battery is exhausted. In addition, this scheme also stores the key ID through the antenna.
                      

                                                   Figure 1 Antenna layout of children's trolley

       
                                                  Figure 2 Actual installation of children's trolley

 

2. Introduction to functions：

(1) Keychain storage ：

When burning the software for the first time, the key pairing must be performed. The MCU will save the successfully matched key ID, and the power-down will not be lost. After that, the functions of PKE, PKG, RKE, and IMMO will all operate with the stored ID. If you want to change the key ID, you only need to re-pair it.

(2) PKE function ：

This function is triggered by pulling the car door handle (no need to control the key button), the base station master commands the low-frequency board to send an RSSI measurement command, after which the key starts RSSI detection, and then the test result is transmitted back through UHF, and the base station master determines whether the key is in the car or outside the car. If it is outside the car, HT-3 certification will begin, and the door will open if the certification is passed.

(3) PKG function：

This function is similar to PKE. When the driver presses the “one-button start” button, RSSI detection will be triggered, but only when the key is in the car, HT-3 authentication will start, and the engine can only be started if the authentication is passed; otherwise, the engine is still locked.

(4) IMMO function：

The operation of PKE and PKG requires battery power. Once the key battery is exhausted, you need to use a conventional car key to replace the PKE function; the PKG function can be replaced by the IMMO function. At this time, you need to keep the key close to the IMMO antenna. If the received key ID is correct and the HT-3 certification result is met, the engine can be started.

(5) RKE function：

Press the key button, the key terminal can send a rolling code through UHF, which contains IDE, Button ID, Sequence response and other data. After the base station master determines that the data is valid, it will perform the corresponding functions (switch the door, trunk, etc.), so as to achieve the purpose of remote control of the car with the key.

 
3. Hardware description：

                                                                      Base station main control board & low frequency board

1) MCU S32K144 , SPI interacts with the low-frequency board through SPI, and can perform corresponding actions based on the response.
2) NJJ29C2 , low-frequency board MCU , can SPI perform low-frequency signal transmission and other operations according to the prescribed SPI protocol.
3) The main control board of the base station and the low frequency board 12V are powered by 12V.
4) S32K144 reset button.
5) SPI interface, which can transmit NXP 制定的 the SPI protocol formulated by NXP to ensure that R98 welding has a 0 Ω resistance.
6) Debugging interface, SWD interface.
7) UART interface, connect to the computer USB , PC and display the operating status of the function board from the PC side.
8) UHF Receiver NCK2912 connection port.
9) 9 sets of LF antenna connectors.
10) SW3 is used to store the key ID . When you just burn the software, be sure to press SW3 first to store the key ID .
11) TP9 , used to simulate the “one-key start" button, when the input is high potential, the PKG function is triggered.
12) TP11 , simulates the action of pulling the door, and when the input is high potential, the PKE function is triggered.
13) SW2, used to trigger the verification PKE function.

Fourth, the operation instructions：
1. Hardware assembly and power-up effect

The main control of the base station, the low-frequency board, the UHF receiver, the key, and the antenna assembly effect are shown in Figure 3.
                  

                                                          Figure 3   PEPS hardware environment construction

The first time you burn the program, the prompt shown in Figure 4 will appear on the base station OLED. At this time, you can hold the WPI key close to the TX9/RX1 IMMO antenna, and then press SW3 to start storing the key ID.
                                                     

                                                      Figure 4  For the first time, the key ID storage prompt is displayed for the first time

After storing the key ID that supports HT-3 authentication in the analog EEPROM area of S32K144, reset S32K144, and the base station OLED will display the operation instructions, as shown in Figure 5. IT SHOULD be noted that “SW(CAR):PKG” means that the TP9 of the function board needs TO be set high to trigger the PKG function; “SW2:PKE" means that the PKE function can be triggered through SW2. OF COURSE, if the child car is installed with the system, the PKE will be triggered through TP11.It is more in line with the application scenarios of PKE.

                                                     

                                             Figure 5  The initial interface of the base station OLED after storing the key ID
At this time, the state jumps caused by different operations, as shown in Figure 6.
                              

                                                               Figure 6  Operation conversion diagram

2. Key ID storage
If you want to store or replace a new key ID, you can hold the key close to the TX9/RX1 antenna, and then click the base station SW3 button to obtain the key ID through IMMO to achieve ID storage. OLED will display whether the storage is successful and the ID number of the key, as shown in Figure 7.

                                                       
                                                         Figure 7  The key ID storage (update) is successful

3. PKG function

TP9 input is high (equivalent to pressing the “one-key start” button), TX1 + TX2 sends an RSSI measurement command and a long carrier signal, and the base station determines whether the key is in the car or outside the car based on the RSSI value measured by the key. If the key is in the car, TX6 will start HT-3 authentication to avoid the possibility of artificially sending false RSSI values. If the authentication is passed, the engine starts, and the OLED display information is shown in Figure 8.
                                                        

                                                         Figure 8  Engine start (distance is for reference only)
Conversely, if the key is outside the car, the engine is still locked when the “one-button start” is pressed, as shown in Figure 9.

                                                           
                                                         Figure 9 Engine locked (distance is for reference only)

4. IMMO function

The TP9 input is high (equivalent to pressing the “one-key start” button). If the key is dead at this time, you need to hold it close to the TX9/RX1 antenna to start the IMMO certification. If the certification is passed, the engine will start. The OLED display is shown in Figure 10.

                                                        
                                                   Figure 10 The key is close to the antenna to start the engine (IMMO)

If the key is not detected, or the authentication fails, the user will be prompted to try again, as shown in Figure 11.

                                                          
                                                             Figure 11  IMMO engine failed to start

5. PKE function

TP11 inputs a high level (equivalent to pulling the door handle), and the key will start to detect the RSSI value based on the low-frequency signal. If the base station determines that the key is outside the car, TX3 will send a low-frequency signal. After the key receives the signal, HT-3 authentication will begin. If the certification is passed, the door opens. The OLED display is shown in Figure 12.

                                                          
                                                         Figure 12  “Pull” the door handle, PKE trigger

6. RKE function

In the absence of operation on the base station, you can press the key button to command the base station to perform RKE operation. If it is a key stored in advance, the RKE can be successfully executed. The base station will obtain the key value and perform the corresponding operation. The OLED display is shown in Figure 13.

                                                          
                                                    Figure 13  The key ID matches, and the base station performs the corresponding functions

If you use another key that is not stored, it will prompt that the key buttons do not match, and the OLED display is shown in Figure 14.

                                                          
                                                        Figure 14 The key ID is inconsistent and the RKE failed