Using MAX 3000A Devices as a Microcontroller I/O Expander

Transcription

1 Using MAX 3000A Devices as a Microcontroller I/O Expander August 2003, Ver 1.0 Application Note 265 Introduction Advantages of Using MAX 3000A Devices Many microcontrollers and microprocessors limit I/O ports and pins to conserve pin counts and reduce package sizes. For many microcontroller (e.g., PIC, 051, and SX) or microprocessor basedsystems, the system design requires more I/O ports or pins than the microcontroller provides. To increase the number of I/O pins without changing the microcontroller, I/O expansion provides a solution. With up to 20 I/O pins and MultiVolt TM I/O capability, Altera MAX 3000A devices allow you to implement microcontroller I/O expansion in microcontroller or microprocessorbased systems. This application note explains how to implement a microcontroller I/O expander in MAX 3000A devices. A key advantage of using MAX 3000A devices as a microcontroller I/O expander is the integration of logic functions across your entire board. The flexibility of a programmable device means that not only can the I/O expansion function be implemented, but other functions can be integrated such as LED drivers or busbridging logic. This integration allows you to reduce component count across the board, minimizing cost and maximizing board space efficiency. Another advantage in using MAX 3000A devices is the MultiVolt I/O capability which enables MAX 3000A devices to interface to 5.0V, 3.3V, and 2.5V I/O pins. This capability allows you to implement voltagelevel shifting to interface older 5.0V devices with newer 3.3V or 2.5V devices or microcontrollers. The large numbers of I/O pins on MAX 3000A devices make it an ideal device for microcontroller I/O expansion. Table 1 shows the maximum user I/O pins available in MAX 3000A devices. The maximum I/O pins available are 20 which translates to 26, bit ports. Additionally, insystem programmability (ISP) means that these features come with the flexibility of reprogrammability on the board. Table 1. Maximum User I/O Pins in MAX 3000A Devices EPM3032A EPM3064A EPM312A EPM3256A EPM3512A Maximum User I/O Pins Altera Corporation 1

2 Implementing a Microcontroller I/O Expander in MAX 3000A Devices The I/O expander design example includes four ports (A, B, C, and D) which can be independently programmed as I/O ports. Each port is bits wide and is bidirectional, becoming an input port when tristated. You can connect the microcontroller unit (MCU) port to or from any port (A, B, C, or D) to perform read and write operations. Figure 1 shows the block diagram of the design example for the microcontroller I/O expander. Figure 1. Block Diagram for Microcontroller I/O Expander Design Example in MAX 3000A Devices Input Data Latch Port A Port B MCU Port I/O Ports 4 2 I/O Setting Data Register 2 4 I/O Ports Output Data Latch Port C Port D CS RST CONF LOAD WR RD MODE 2 Altera Corporation

3 Table 2 lists all the functions of the input and output pins. Table 2. Input & Output Pins in a Microcontroller I/O Expander Example Design I/O Name Type Description Active MCU port Bidirectional bit bidirectional data lines that interface with the MCU data bus. The bit data can be written into or read out of the microcontroller I/O expander on the WR and RD signals. Configuration data is also transmitted through this port. The MODE signal determines whether the MCU port is a data or address bus. CS Input Input signal to select the device. Low RST Input Input signal to reset the device and all internal Low registers. CONF Input This control signal stores the sddress[5..0] from the MCU port on the falling edge of CONF into the configuration registers. Data on address[7..6] is ignored. (The operation will be discussed later in this application note.) LOAD Input This control signal stores the address[1..0] from the MCU port on the falling edge of LOAD into configuration registers. Data on address[7..2] is ignored. (The operation will be discussed later in this application note.) WR Input Input signal that causes the data on the MCU port to be written to the enabled port (A, B, C, or D). RD Input Input signal that enables the data bus transfer to the MCU port from the enabled port (A, B, C, or D). MODE Input Tristates the MCU port when this signal is high. The MCU port setting (input or output) depends on the configuration registers when MODE is low. Port A Bidirectional bit, generalpurpose I/O port that can be programmed to either output or input mode. Port B Bidirectional bit, generalpurpose I/O port that can be programmed to either output or input mode. Port C Bidirectional bit, generalpurpose I/O port that can be programmed to either output or input mode. Port D Bidirectional bit, generalpurpose I/O port that can be programmed to either output or input mode. Low Low Low Low Altera Corporation 3

4 Functional Description The microcontroller I/O expander operates as a slave that sends and receives data through the MCU port. Data is sent through the I/O expander at the hightolow transition of the WR signal (with CS set to low) and received at the hightolow transition of the RD signal (with CS set to low). Write Mode In write mode, the selected port (A, B, C, or D) is configured as an output port and the MCU port as an input port. Therefore, when the RW signal changes from high to low (with CS set to low), the data from the MCU port is written into the output data latch of the selected port. Read Mode In read mode, the selected port (A, B, C, or D) is configured as an input port and the MCU port as an output port. When the RD signal changes from high to low (with CS set to low), the data from the selected port is written into the input data latch of the MCU port. 1 During read and write operation, the MODE signal control pin must be set to low. See Design Verification on page 6 for an example of read and write operations. Configuration of the Microcontroller I/O Expander Configuration of the microcontroller I/O expander is used to determine whether the port is input or output and enabled or disabled. Activation of the new configuration occurs with a single configuration pulse of the CONF signal. Data controlling the microcontroller I/O expander is stored in a set of 6bit registers. Data to be written into these registers, consisting of 4 bits for I/O port configuration data and 2 bits for the enabled port address data, is placed on the input address bus (MCU port) with the MODE signal set to high and the CS signal set to low. Input data is stored in the configuration registers at the hightolow transition of the CONF signal input pin with the CS signal set to low. This transition causes the state of the microcontroller I/O expander to be set to the selected configuration. When the LOAD signal is asserted from high to low (with CS set to low), only 2 bits of the enabled port address data (bit1 and bit0) are stored in the configuration registers. Use the LOAD signal when you need to select the enabled port to perform read or write operation instead of configuring the ports. Figure 2 shows the functionality of every bit in the address bus during configuration mode. 4 Altera Corporation

5 Figure 2. I/O Expander Address Bus Configuration Function A7 A6 A5 A4 A3 A2 A1 A0 bit 76: bit 5: bit 4: bit 3: bit 2: bit 10: A7:A6: No functionality A5: Port D configuration bit 0 = Configured as input 1 = Configured as output A4: Port C configuration bit 0 = Configured as input 1 = Configured as output A3: Port B configuration bit 0 = Configured as input 1 = Configured as output A2: Port A configuration bit 0 = Configured as input 1 = Configured as output A1:A0: Port Address Table 3 shows the address contents to enable the particular I/O ports. Table 3. Port Addresses A1:A0 Port 00 A 01 B 10 C 11 D MCU port direction, input or output, cannot be directly configured by the user. It is configured internally by the selected enabled port. For example, if the enabled port is in input mode, the MCU port is set to an output mode. However, you can use the MODE signal control pin to tristate the MCU port so that it becomes an input port, allowing you access to the configuration registers. Reset mode is also supported in the microcontroller I/O expander reference design. When the RST signal is asserted (with CS set to low), the contents of all registers are reset to zero and the entire I/O expander is in its initial state, where all the ports (including the MCU port) are set to input mode. Altera Corporation 5

6 MAX 3000A Implementation The microcontroller I/O expander design example was targeted to 12macrocell MAX 3000A devices (EPM312ATC100) using the Quartus II software. The design utilization in the 12macrocell MAX 3000A device is shown in Table 4. The data in Table 4 shows that there is sufficient resources (I/O pins and macrocells) remaining in the device for the implementation of the other logic in the system. Table 4. Microcontroller I/O Expander EPM312A Utilization Resource Available Used Utilization (%) Macrocells Flipflops I/O Pins Design Verification Design verification of a microcontroller I/O expansion was accomplished by using the Quartus II software. The design was verified both in functional and timing simulation in MAX 3000A devices (EPM312ATC100). Figures 3 and 4 show the timing simulation of the microcontroller I/O expansion during read and write operation. 6 Altera Corporation

7 Figure 3. Microcontroller I/O Expansion Write Mode Timing Simulation Configure the Microcontroller I/O Expander The HightoLow Transition of the WR Signal Creates New Output Values Change the Enabled Port The WR Signal Creates New Output Values With all the I/O pins in tristate mode, each port is initialized. After initialization, Port A and Port B are configured as output, Port C and Port D are configured as input, and Port B is enabled for write operation. When the WR signal asserts a hightolow transition, the MCU port data (146) is latched to the output Port B. In the last section of simulation, Port A is enabled at the hightolow transition of the LOAD signal. When the WR signal asserts a hightolow transition, the MCU port data (10) is latched to the output Port A. Altera Corporation 7

8 Figure 4. Microcontroller I/O Expansion Read Mode Timing Simulations The RD Signal Creates New Output Values Configure the Microcontroller I/O Expander The HightoLow Transition of the WR Signal Creates New Output Values Change the Enabled Port With all the I/O pins in tristate mode, each port is initialized. After initialization, all ports (A, B, C, and D) are configured as input and Port C is enabled for read operation. When the read signal asserts a hightolow transition, the Port C data is latched to the MCU port. While in the last part of the simulation, Port D is enabled at the hightolow transition of the LOAD signal. When the RD signal asserts a hightolow transition, the Port D data (146) is latched to the MCU port. Altera Corporation

9 Microcontroller I/O Expander Applications Figures 5 shows how to increase the microcontroller s I/O ports using the I/O expander. This microcontroller I/O expander can be targeted or modified to target to any bit microcontroller (e.g., PIC and 051). Figure 5. Application of Microcontroller I/O Expander Microcontroller I/O Expander RD output WR output RD WR Port A CS output LOAD output CS LOAD Port B CONF output MODE output CONF MODE Port C RST output Microcontroller I/O Port RST MCU Port Port D Conclusion With up to 20 I/O pins and MultiVolt I/O capability, Altera MAX 3000A devices allow you to implement microcontroller I/O expansion in a single device. MAX 3000A devices enable you to design custom microcontroller I/O expanders with additional features other than the example provided in this application note. Altera Corporation 9

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