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IrDA 1.x System Implementation

IrDA-1.0 System Implementation
IrDA-1.1 System Implementation
External Connection
System Hardware Testing
Conclusion

IrDA-1.0 System Implementation

To implement IrDA capability into systems like notebook PCs, PDAs, etc., one needs to use the digital interface chip and an analog front-end component. IrDA-1.0 digital chips in the form of super I/O chips are provided by National Semiconductor, SMC, Winbond, etc. Analog module are in two forms: chips or optoelectronic modules. Analog chips are supplied by Irvine Sensor, Unitrode, Rohm and Crystal Semiconductor (which has an integrated mixed-signal analog/digital chip) where additional IR-LED and detector diode are needed and careful PCB layout around the sensitive detector circuitry is required. Optoelectronic modules are provided by HP , Temic, Siemens, Sharp, etc. which integrate the analog chip with the IR-LED and diode in one compact module with various pinout configurations. The system implementation of IrDA- 1.0 is straightforward. The only inconvenience is the need to implement in IrDA application software (e.g. Windows 95 -IR driver from Microsoft or Tranxit file transfer software from Puma Technology) the respective hardware device driver to program speeds for each hardware systems. For IrDA-enabled portable devices that do not use Windows operating system, special IrDA protocol engine (stack) in either C or assembly codes need to be built in. Due to their limitation of low-power, slow CPU, limited memory, very compact IrDA protocol stack is required. ACTiSYS has successfully licensed their protocol stack in C or various assembly codes (model # ACT- IR920SW-IR960SW) to many OEM manufacturers of cellular phones, pagers, printers, portable instruments, portable storage devices, handheld PCs, etc. The code compactness is represented by one of their model, ACT-IR920SW (8031 code for peripherals) that is only 3.8 KBytes.

IrDA-1.1 System Implementation
Aside from the differences in the Physical Layer, The IrLAP, IrLMP, and upper layers of IrDA-1.0 and IrDA-1.1 are almost identical. By design, IrDA-1.1 is also backward compatible with IrDA-1.0. However, due to the much higher data rate allowed in IrDA-1.1, there are both hardware and software implications. For the 115.2 kbps top data rate used in IrDA-1.0, most computers and micro- controllers only need very minimum hardware and can use the CPU to handle the byte stuffing or removal and the CRC calculations. Low end micro-controllers such as 22 MHz 80C51 and 12 MHz Z80 has been successfully used to implement IrDA secondary stations at 115.2 kbps. The hardware needed consists of a UART (which most computers and micro-controllers may already have), a simple encoder/decoder circuit and the IR transceiver. For the 1.152M and 4.0 Mbps data rate used in IrDA-1.1, a packetizer must be used and the encoder/decoder circuit is more complex. The IR transceiver must also be capable of handling the faster speed. In most of the cases, DMA needs to be used to transfer data from the packetizer to and from memory. Even through there is no significant changes in the IrLAP, IrLMP, and upper layers of the protocol from IrDA-1.0 to IrDA-1.1, software efficiency must also be considered. For example, at 115.2 kbps, it takes about 100 msec to transmit a 1 KByte frame. Thus a 2 msec software overhead will only cause a 2 % degradation in performance. At 4 Mbps, however, it takes only 2 msec to transmit the same 1 KByte frame and the same 2 msec software overhead will cause a 100 % degradation in performance. In order to take advantage of the higher raw data rate, IrDA-1.1 software must be more efficient or be assisted by hardware.

External Connection

To implement IrDA-1.0 external adapters to be attached to the RS232 serial port, the challenge is to reach a long distance with reliable IR connection sustainable at 115.2Kbps baud rate, using only the limited current supplied from the RS232-port signal lines. This current is typically in the range of 10mA which needs to be booted up to around 21mA average current at 115.2Kbps rate in order to provide reliable IR communication at distance of 1 meter. ACTiSYS has successfully accomplished this with their ACT-IR220L serial adapter which offers 2.4 meter reliable IR link distance in most applications using no external power. For the Japanese market where ASK- IR modulation and protocol specification has long been used in consumer electronic devices like organizers, etc. It is very desirable to have both IrDA and ASK dual modes in the IR interface device. One example is the ACTiSYS ACT-IR200L dual- mode serial adapter. It also maintains the company tradition of long IR communication distance using only RS232-port signal power and no external power source. For implementing IrDA-1.0 external adapter for printer and other peripherals, compact IrDA protocol stack needs to be built into the adapter. Some examples are ACTiSYS's ACT-IR100X and IR100M printer adapters. To implement IrDA-1.1 (1.152M and/or 4M bps) external serial adapter, RS232 port is too slow. There are four options: internal add-on card, special IrDA connector, enhanced parallel port, special serial port like Universal Serial Bus (USB), etc. All these options are being explored by many of the current IrDA adapter suppliers. Example is ACTiSYS's ACT-IR2000 series. To implement IrDA-1.1 external adapters for printers, peripheral devices or wired LAN, the appropriate IrDA protocol stacks need to be built into the adapters. Examples are the LAN adapter from Extended Systems and ACTiSYS (ACT- IR1000M and IR6000N).

System Hardware Testing
The common problem faced by many of the IrDA-enabled systems manufacturers is the long IrDA test bottleneck on the production line. They usually use the commercially available IrDA-compliant application software or even the non-IrDA compatible file transfer software. To shorten the test time, they use very short test file. The problem is long test time (~1 minute), no easy reading and unreliable test of error rate at different speeds, no parameter re- setting by QA engineer, no isolation of send or receive problem, no automatic recording of test results. Recently, there are specific IrDA system hardware test software available to solve all these critical problem. Example is ACTiSYS's ACT-IR900SW which requires 5~10 sec. per test system to automaticall print and record the error rates. It has special test patterns to exercise stress test on IrDA hardware. It can even test both IrDA and ASK modes. Its extension, IR9000SW will test IrDA-1.1 enabled system hardware and is being tested on the newly available IrDA-1.1 adapters.

Conclusion
We have described here the basics of IrDA-1.0 and IrDA-1.1 protocol, system implementation, external connection and system hardware testing. The components for both IrDA generations will become easily available and their cost reduced very quickly. The percentage of IrDA-enabled mobile and desktop computers will increase very quickly. This will expand soon into the various vertical markets of non-computer industries. The IrDA-compliant application software, the protocol stacks for controller environment and system hardware testing software have been the show stopper. This situation is improving quickly and should accelerate the rate of IrDA implementation into new systems. Many new IrDA applications in video conferencing, ISDN-, PBX-link will also emerge. The new challenge for IrDA community is the incorporation of and co- existence with consumer IR (usually longer distance, higher power and lower baud rate) applications and future higher speed (perhaps 15 Mbps or higher) extension.

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