SPX-5 Reference Manual
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Introduction
Description
The VersaLogic SPX-5 is an 8-channel FET switch expansion module designed to be used with
EBX-11 Rev 6.xx SPX™ enabled base boards. Its features include:
Freescale MC33879 Octal Serial Switch
8 High-side/Low-side FET Switches
Load/Fault Detect
24VDC Working Voltage
2 Inputs Configurable for PWM
0.6A – 1.2A Current Limit
VersaLogic SPX boards are a line of I/O expansion boards using the industry standard Serial
Peripheral Interface (SPI) bus. These are small 1.2” x 3.775” boards that can be mounted on the
PC/104 and PC/104-
Plus
stack using normal standoffs. They can also mount up to two feet away
from the base board using custom cabling.
SPX boards are electrically connected to a base board via a 14-pin 2 mm cable. Up to four boards
can be daisy-chained together. The SPI bus requires each chip to have a discrete chip-select
signal, and the 14-pin interface supplies four chip-select signals. The maximum clock rate is 8
MHz.
Power for SPX boards is supplied through the interface cable. I/O connections on SPX boards
are provided through screw terminal/wire connections.
All SPX boards are RoHS compliant and industrial temperature rated.
A
BOUT
SPI
The SPI bus specifies four logic signals: SCLK – Serial clock (output from master); MOSI –
Master output, slave input (output from master); MISO – Master input, slave output (output from
slave); and SS – Slave select (output from master).
The SPI implementation on VersaLogic CPU boards adds additional features, such as hardware
interrupt input to the master. The master initiates all SPI transactions. A slave device responds
when its slave select is asserted and it receives clock pulses from the master.
Slave selects are controlled in one of two modes: manual or automatic. In automatic mode, the
slave select is asserted by the SPI controller when the most significant data byte is written. This
initiates a transaction to the specified slave device. In manual mode, the slave select is controlled
by the user and any number of data frames can be sent. The user must command the slave select
high to complete the transaction.
The SPI clock rate can be software configured to operate at speeds between 1 MHz and 8 MHz.
All four common SPI modes are supported through the use of clock polarity and clock phase
controls.
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