Rice Lake Motorola DS457 Laser Scanner - Manual (Page 127)

CHAPTER 8 SSI INTERFACE
Introduction
This chapter describes the system requirements of the Simple Serial Interface (SSI), which provides a
communications link between Motorola decoders (e.g., scan engines, imagers, hand-held scanners,
two-dimensional scanners, hands-free scanners, and RF base stations) and a serial host. It provides the
means for the host to control the imager.
Communications
All communication between the imager and host occurs over the hardware interface lines using the SSI
protocol. Refer to the
Simple Serial Interface Programmer’s Guide
, p/n 72-40451-xx, for more information on
SSI.
The host and the imager exchange messages in packets. A packet is a collection of bytes framed by the proper
SSI protocol formatting bytes. The maximum number of bytes per packet that the SSI protocol allows for any
transaction is 257 (255 bytes + 2 byte checksum).
Decode data can be sent as ASCII data (unpacketed), or as part of a larger message (packeted), depending on
the imager configuration.
SSI performs the following functions for the host device:
•
Maintains a bi-directional interface with the imager
• Allows the host to send commands that control the imager
•
Passes data from the imager to a host device in SSI packet format or straight decode message.
The working environment of the SSI consists of an imager, a serial cable which attaches to the host device,
and in some instances, a power supply.
SSI transmits all decode data including special formatting (e.g., AIM ID). Parameter settings can control the
format of the transmitted data.
The imager can also send parameter information, product identification information, or event codes to the host.
All commands sent between the imager and host must use the format described in the SSI Message Formats
section.
SSI Transactions on page 8-3
describes the required sequence of messages in specific cases.