410-063 Digilent

1300 Henley Court Pullman, WA 99163 509.334.6306 www.digilentinc.com PmodDA1 Reference Manual Revised May 24, 2016 This manual applies to the PmodDA1 rev. C Overview The Digilent PmodDA1 is an 8-bit Digital-to-Analog Converter module that can output up to four different analog signals simultaneously. This module is ideal for users who want to output a variable voltage signal but do not want to use up their system board s analog capable pins. Features include: Two 8-bit DACs Four D/A conversion channels Maximum conversion rate of 1.875 MSa Small PCB size for flexible designs 1.0 0.8 (2.5 cm 2.0 cm) 6-pin Pmod connector with GPIO interface Library and example code available in resource center The PmodDA1. 1 Functional Description The PmodDA1 converts an 8-bit digital input signal to a corresponding analog output voltage ranging from 0 to Vdd. Each of the two AD7303s on this Pmod have two 8-bit DACs allowing the user to select which DAC they want their stream of data to be passed through. Because each chip is double buffered, users may also choose to send two separate streams of data on an input and then update the two corresponding outputs simultaneously. 2 Interfacing with the Pmod The PmodDA1 communicates with the host board via an SPI-like communication protocol. The difference between the standard SPI protocol and this protocol is manifested in the pin arrangement on this Pmod. A typical SPI interface would expect a Chip Select, a Master-Out-Slave-In, a Master-in-Slave-Out, and a Serial Clock signal. However, with the two DACs on this chip, both of the data lines (MOSI and MISO) are designed to operate only as inputs, making them both Master-Out-Slave-In data lines. Copyright Digilent, Inc. All rights reserved. DOC : 502-063 Page 1 of 3 Other product and company names mentioned may be trademarks of their respective owners. PmodDA1 Reference Manual The PmodDA1 will receive its 8 bits of information from the system board through 16 clock cycles with first eight bits consisting of eight control bits and the remaining eight bits representing the 8 bits of the data with the MSB first. Each bit is received by the rising edge of the serial clock line. The function dictated by the first eight control bits is executed when the chip select line is brought high. A pinout table and diagram for the PmodDA1 are provided below: Header J1 Pin Signal Description 1 ~SYNC Chip Select (active low) 2 D0 Input Data 1 3 D1 Input Data 2 4 SCK Serial Clock 5 GND Power Supply Ground 6 VCC Power Supply (3.3V/5V) Header J2 Pin Signal Description 1 A1 Output Data A1 2 B1 Output Data B1 3 A2 Output Data A2 Figure 1. PmodDA1 circuit diagram. 4 B2 Output Data B2 5 GND Power Supply Ground 6 VCC Positive Power Supply Table 1. Connector J1: Pin descriptions as labeled on the Pmod. The on-board DACs can in principle use either an external or internal reference voltage however, the PmodDA1 is designed that the internal reference voltage of Vdd/2 volts must be used. Because of this, the first bit in the command signal sent to the Pmod must always be a logic low signal in order to use the internal reference voltage on the DAC. Tables describing the command signal and the associated bits from the AD7303 datasheet are provided below. Control Bits Data Bits ~INT/EXT X LDAC PDB PDA ~A/B CR1 CR0 DB7 DB6 DB5 DB4 DB3 DB2 DB1 DB0 (MSB) (LSB) Table 2. PmodDA1 input shift register structure. Note: The signifies that the signal is active when driven low. Copyright Digilent, Inc. All rights reserved. Page 2 of 3 Other product and company names mentioned may be trademarks of their respective owners.