The Parallel Slave Port (PSP) is a feature found in some Microchip PIC microcontrollers, particularly in the PIC16 and PIC18 families. It allows the microcontroller to interface with external devices in a parallel communication scheme, acting as a slave device. Here’s a detailed explanation of its features:
1. 8-bit Wide Data Port
- The PSP is an 8-bit bidirectional port, meaning it can transmit and receive 8 bits of data simultaneously.
- This makes it suitable for interfacing with devices that use parallel communication, such as external memory, LCDs, or other microcontrollers.
2. External Control Signals
The PSP relies on three external control signals to manage data transfer:
- RD (Read):
- When asserted (typically active low), it indicates that the external master device wants to read data from the PSP.
- The microcontroller places the requested data on the 8-bit PSP data bus.
- WR (Write):
- When asserted (typically active low), it indicates that the external master device wants to write data to the PSP.
- The microcontroller reads the data from the 8-bit PSP data bus.
- CS (Chip Select):
- This signal enables or disables the PSP. When asserted (typically active low), the port is active and ready to communicate.
- When de-asserted, the PSP is disabled, and the data pins can be used for other purposes (e.g., general-purpose I/O).
3. Operation as a Slave Device
- The PSP is designed to operate as a slave in a master-slave communication system.
- The external device (e.g., a microprocessor or another microcontroller) acts as the master and controls the communication by asserting the RD, WR, and CS signals.
- The PIC microcontroller responds to these signals by either sending or receiving data.
4. Bidirectional Data Transfer
- The PSP can both send and receive data, making it versatile for various applications.
- The direction of data flow is determined by the RD and WR signals from the external master device.
5. Interrupt Capability
- The PSP can generate an interrupt when a read or write operation occurs.
- This allows the microcontroller to respond quickly to data transfer requests without constantly polling the PSP.
6. Use Cases
- The PSP is commonly used in applications where the PIC microcontroller needs to interface with external devices that use parallel communication, such as:
- External memory (e.g., SRAM, EEPROM)
- LCD displays
- Other microcontrollers or microprocessors
7. Configuration
- To use the PSP, specific registers in the PIC microcontroller must be configured:
- TRISE Register: Configures the PSP pins as inputs or outputs.
- ADCON1 Register: Disables analog functionality on the PSP pins (if applicable).
- PSPMODE Bit: Enables the PSP functionality.
What Makes the Parallel Slave Port (PSP) Special?
The PSP is a pretty neat feature, especially if you’re working on projects that require fast, parallel data transfer. Here’s what it brings to the table:
- 8-Bit Data Transfer: It can send and receive 8 bits of data at once, making it ideal for interfacing with devices like external memory, LCDs, or even other microcontrollers.
- External Control Signals: It uses three key signals to manage communication:
- RD (Read): Tells the PIC to send data.
- WR (Write): Tells the PIC to receive data.
- CS (Chip Select): Enables or disables the PSP.
- Bidirectional Communication: It can both send and receive data, depending on what the external device needs.
- Interrupt Support: It can generate interrupts, so your microcontroller doesn’t have to constantly check for data—it just gets notified when something happens.
Do Other Microcontrollers Have Something Similar?
Absolutely! While the PSP is specific to PIC microcontrollers, many other microcontroller families offer similar functionality, though they might call it something else. Here are a few examples:
1. AVR Microcontrollers
- AVR microcontrollers, like the popular ATmega series, have an External Memory Interface (EMIF). While it’s mainly designed for connecting to external memory, it can also handle parallel communication with other devices. It uses signals like RD, WR, and ALE (Address Latch Enable) to manage data transfer.
2. ARM Microcontrollers
- ARM-based chips, such as STM32 or NXP’s LPC series, often include a Flexible Static Memory Controller (FSMC) or External Bus Interface (EBI). These are super versatile and can handle parallel communication with a wide range of devices, from memory chips to LCD displays. They use signals like CS, OE (Output Enable), and WE (Write Enable).
3. 8051 Microcontrollers
- The classic 8051 microcontroller family doesn’t have a dedicated PSP, but its general-purpose I/O ports (like Port 0 and Port 2) can be configured for parallel communication. With a little extra work, you can use these ports to interface with external devices.
4. Renesas Microcontrollers
- Renesas microcontrollers, like the RX or RL78 series, often come with a Bus Interface Unit (BIU) or External Bus Interface. These are designed for parallel communication and support control signals like RD, WR, and CS.
5. Texas Instruments Microcontrollers
- TI’s MSP430 and Tiva C Series microcontrollers also support parallel communication through their External Memory Interface or general-purpose I/O ports. They’re flexible enough to handle a variety of parallel communication tasks.
Why Does This Matter?
If you’re designing a system that needs to communicate with external devices, parallel communication can be a great choice. It’s fast, straightforward, and widely supported across different microcontroller families. Whether you’re using a PIC with its PSP or an ARM chip with an FSMC, you’ve got options.
The key takeaway? The PSP isn’t unique to PIC microcontrollers. Many other architectures offer similar features, though they might go by different names or have slightly different implementations. So, if you’re ever working on a project and need parallel communication, don’t worry—you’ve got plenty of choices!
Also read: Difference between ARM and Thumb states (ARM vs. thumb)