We can Read Locked Microchip PIC18F4321 Heximal, please view the PIC18F4321 features for your reference:

the state of these flag bits, taken together can be read to indicate the type of Reset that just occurred. This is described in more detail in Section 4.6 “Reset State of Registers”. The RCON register also has control bits for setting
interrupt priority (IPEN) and software control of the BOR (SBOREN). Interrupt priority is discussed in Section 10.0 “Interrupts”. BOR is covered in Section 4.4 “Brown-out Reset (BOR)”.

The MCLR pin provides a method for triggering an external Reset of the device. A Reset is generated by holding the pin low. These devices have a noise filter in  the MCLR Reset path which detects and ignores small pulses. The MCLR pin is not driven low by any internal Resets, including the WDT when Read Locked Microchip PIC18F4321 Heximal.

In PIC18F1230/1330 devices, the MCLR input can be disabled with the MCLRE Configuration bit. When MCLR is disabled, the pin becomes a digital input. See Section 9.1 “PORTA, TRISA and LATA Registers” for more information. A Power-on Reset pulse is generated on-chip whenever VDD rises above a certain threshold. This allows the device to start in the initialized state when VDD is adequate for operation.

To take advantage of the POR circuitry, tie the MCLR pin through a resistor (1 kÙ to 10 kÙ) to VDD. This will eliminate external RC components usually needed to create a Power-on Reset delay. A minimum rise rate for VDD is specified (parameter D004). For a slow rise time, see Figure 4-2. When the device starts normal operation (i.e., exits the Reset condition), device operating parameters (voltage, frequency, temperature, etc.) must be met to ensure operation. If these conditions are not met, the device must be held in Reset until the operating conditions are met if Read Locked Microchip PIC18F4321 Heximal.

POR events are captured by the POR bit (RCON<1>). The state of the bit is set to ‘0’ whenever a Power-on Reset occurs; it does not change for any other Reset event. POR is not reset to ‘1’ by any hardware event. To capture multiple events, the user manually resets the bit to ‘1’ in software following any Power-on Reset after READ MCU.