MCP3901EV-MCU16 Microchip Technology, MCP3901EV-MCU16 Datasheet - Page 15

• Manufacturer Part Number: MCP3901EV-MCU16
• Description: BOARD EVAL FOR 2CH ADC MCP3901
• Manufacturer: Microchip Technology

Specifications of MCP3901EV-MCU16

• Number Of Adc's: 2
• Number Of Bits: 24
• Data Interface: SPI™
• Inputs Per Adc: 1 Differential
• Input Range: ±1 V
• Voltage Supply Source: Analog and Digital
• Operating Temperature: -40°C ~ 85°C
• Utilized Ic / Part: MCP3901
• Silicon Manufacturer: Microchip
• Application Sub Type: ADC
• Kit Application Type: Data Converter
• Silicon Core Number: MCP3901, PIC24F, PIC24H, DsPIC33, PIC18F86J55
• Kit Contents: Board
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

2.1
© 2009 Microchip Technology Inc.
DSPIC33 FIRMWARE DESCRIPTION
2.1.1
After reset, the global variables: ConfigHValue, ConfigLValue, GainValue, and
StatusComValue are written to 0x00. These variables will be written with the values
received from the PC, setting up the MCP3901 the way it is needed. Next, the
Initialization() function is called to set up the dsPIC33. First, the interrupt nesting is
enabled, only to disable the user interrupts by putting the MCU priority 7 (maximum).
External interrupt 3 is enabled on the positive edge. INT3 interrupt is enabled but the
priority is set to 6. Since it is lower than 7, it will not be active until the MCU priority is
decreased under 6. The MCU will use the FRC (7.37 MHz) with PLL. The clock on the
MCU will be 80 MHz, the maximum frequency for dsPIC33, at which the computing
power is 40 MIPS.
Timer 2 is placed on the Output Compare 1 pin (OC1), and is used to generate the
master clock (MCLK) for the MCP3901. In addition, some initial values are set up for
the MCP3901 clock frequency. Timer 5 is configured (but not active), and the interrupt
is disabled. The user can enable it for different applications. SPI peripheral is
configured, but the interrupt is disabled. The SPI interrupt will be enabled in code to
establish the communication between MCU and MCP3901. The UART is used to send
and receive data from the PC at a speed of 115200 baud. Timer 8 and Timer 9 are
configured to create a 32-bit timer that is running at maximum speed. It is used to
measure the time needed to fill the data buffer, so it will measure the sampling speed
of the MCP3901.
After the execution of the Initialization() function, the MCP3901 is configured with
values given by a set of functions, especially developed for the MCP3901
configuration. This step is not necessary in this case because the MCP3901 will update
its configuration using data that is coming from the PC GUI. The functions used here
are very helpful for the users to develop applications that do not involve a PC to
configure the MCP3901.
For example, AddressLoop(NONE) is used to select the loop on specific registers
groups and types. DRHIZ(ON) will allow the Data Ready pulse to be present at the
output of the MCP3901 even if there is no pull up resistor. SetGain(1,1) configures the
gain of both channels at 1, etc. A list of all configuration functions are found in the
firmware file, "main.c", starting at line 345.
It is important to have interrupts disabled, one way or another, during this configuration.
Only after we configure the MCP3901 using the functions mentioned we can enable
interrupts. Here, this is done by decreasing the CPU priority to 3.
Reset and Initialization
Chapter 2. Firmware
MCP3901 ADC EVALUATION BOARD
FOR 16-BIT MCUs USER’S GUIDE
DS51845A-page 11