read barcode from image c#.net FIGURE 7.19 ISA bus signals. in Software

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FIGURE 7.19 ISA bus signals.
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Making Code 128 In None
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176 COMMUNICATION LINKS FOR THE AVR PROCESSOR
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Drawing USS Code 128 In C#
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T1 Clock
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Address Bus
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Making Code 39 Full ASCII In None
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IOR* Valid Data DATA Bus
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Encoding GS1 - 13 In None
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FIGURE 7.20 ISA bus signals during Port Read operation.
Printing Bar Code In None
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Print ECC200 In None
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T1 T2 T3 T4 T5
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Code 128 Scanner In None
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CLOCK
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ADDRESS
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IOW* Valid data
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Generating UPC-A Supplement 2 In None
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DATA
FIGURE 7.21 ISA bus signals during Port Write operation.
UNIVERSAL SERIAL BUS 177
mice, keyboard, stylus, game peripherals, phone, audio, etc. It was designed keeping in mind such low- to medium-speed applications. In this section we are interested in connecting the AVR family of controllers to the USB so as to get a fast interface to the PC. The applications could be to connect a data acquisition system to the PC using the USB, with the AVR as the embedded controller inside the data acquisition system, or to connect a special camera system to the PC through the USB. Figure 7.22 illustrates the possible application space. The USB is a very complex interface and I do not intend to cover it in detail. Actually, it is complex enough to be the subject of another book. In this section, we just want to facilitate awareness of this interface and identify some other chips that can provide conectivity to the AVR series of processors. It would be ideal if the AVR processors had a built-in USB port, but that is not the case with the present generation of AVR processors. The USB interface consists of a single signal in a differential format, as illustrated in Figure 7.23. Together with the data signal, the USB cable also carries power supply for use by the peripheral device. A USB system consists of three components:
1. USB interconnect: This includes the way the devices are connected to each other and
to the host and the way these devices share the channel.
2. USB Host: There is only one host in a USB system, which is the host computer.
USB Port
PC USB Link
AVR hosted Data Acq System
USB Port
AVR hosted Camera PC USB Link
FIGURE 7.22 USB connectivity.
178 COMMUNICATION LINKS FOR THE AVR PROCESSOR
5 meters max.
cable length Wire colors
Vcc D+ DGnd
FIGURE 7.23 USB cable.
3. USB devices: These are the actual function devices (like the mouse) as well as hubs,
which are like extension points for function devices.
Figure 7.24 illustrates the USB bus topology, i.e, the way all the components connect to the PC that is the host. Figure 7.25 shows a hub and how it can connect to the upstream port (the host or another hub) on one end and to actual devices or other downstream hubs on the other end. The communication on a USB occurs between point-to-point segments over the two wires. The USB signaling is of 2 types: full-speed signaling at bit rate of 12 Mbit/s and low-speed signaling at 1.5 Mbit/s. Both modes can coexist in the same USB system by mode switching in a device transparent mode. The clock for the system is transmitted encoded with the data stream using NRZI scheme. Each data packet has a SYNC field to allow receivers to synchronize their clocks. There are many USB-capable processors in the market. Although Intel was the first one to design the USB microprocessors, recently they have discontinued these products and sold the technology to Cypress. Cypress is now a market leader with their CY7C63 series of low-speed USB microcontrollers and CY7C64 series of full-speed microcontrollers as well as the acquisition of Anchor Chips company, which makes 8051 core and USB peripheral function chips. However, the Cypress and the Anchor chips are complete microprocessors and not really suitable to interface with AVR chips, though not impossible. National Semiconductors offers an interesting USB interface chip USBN9602, with a parallel interface as well a MICROWIRE interface specifically to connect to generalpurpose processors, and from the data sheets, seems a very good candidate to connect to the AVR (Figures 7.26 and 7.27.) Another USB controller that goes with a local processor is the NET2888 USB chip from Netchip (www.netchip.com) and can be used together with an AVR processor.
7.10 IrDA Data Link
IrDA stands for Infrared Data Association, which has a charter to create a standard for lowcost Infrared data interconnection. This standard is called IrDA data link and allows a walk-up, point-to-point method of data transfer.
;;;; ;; ; ; ;;
Vcc (Red) D+ (Green) D- (White) Gnd (Black)
IRDA DATA LINK 179
Host
Node
Hub1
Node Hub2
Node
Node
FIGURE 7.24 USB topology.
To Nodes or Hubs
Port1 From Upstream port HUB
Port2 To Nodes or Hubs
Port3
Port4
Port4
To Nodes or Hubs
FIGURE 7.25 A hub.
180 COMMUNICATION LINKS FOR THE AVR PROCESSOR
Parallel Interface Bus to a Microprocessor Media Access Controller Physical Layer Interface Endpoint/Control FIFOs Micontroller Interface USB Transceiver AD0/AD7
ALE CS* WR* RD* MICROWIRE Port 48 MHz
USB event detect
Clock recovery
Clock generator
48 MHz Oscillator
CLKOUT
FIGURE 7.26 USBN9602 block diagram.
8515 X1 ALE WR* RD* PD2(INT0) CLKOUT ALE WR* RD* INTR CS*
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