Pepper Computer Modular Computers RS485 - Manual (Page 83)

SMART I/O User’s Manual
©1996 PEP Modular Computers GmbH March 12, 1996 Page 3 - 5
3
Chapter 3 SMART-EXT
3.3 Functional Description
Figure 3.3.1: SMART-EXT Block Diagram
The SMART-EXT is a carrier board for up to 2 SMART-Modules with data
transfer between SMART-BASE and EXT units being performed by the
interface connector incorporating the Motorola synchronous Serial Peripheral
Interface (SPI).
The maximum bit transfer rate is set to 1 MHz which ensures a typical
response time from an addressed extension slot of approximately 50 µ s.
The MCU (Micro Controller Unit - 68HC05C4) handles the SPI transfers
and the slot-dependent commands and actions through the SMART-EXT
firmware burned into the MCU mask or in an OTP (One-Time Programma-
ble) PROM area.
In order to communicate with a particular SMART-EXT slot, a specific PEP
defined protocol has to be observed. All necessary functions are provided in
the OS-9 ‘C’ library SMAC.L which should be included when writing a
specific C’ application program.
Slot Detect
Logic and
Buffer
Slot
A
Slot
B
Interface
Connector
with
Integrated
SPI
Interface
Connector
with
Integrated
SPI