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S PECIFICATIONS I/O Interface Connections and Signals The 14 bit (max) absolute position data is provided in two bytes. The Low and High bytes are expressed on the 8 data lines by asserting the active low output enable signals OEL and OEH, respectively. OEL also functions as a latch signal telling the decoder to latch the current encoder position data. Therefore they must be read in a specific order: Low byte first followed by the high byte is the default scheme--which the demonstration display is hardwired to execute. Every subsequent read of the Low byte will latch the encoder's new position data, whether the High byte has been read or not. The table below describes the usage of the Output Enables and Data lines.Some microcontrollers expect High byte first when concatenating a 16 bit word from 2 bytes. If the user wishes to read High byte first, thereby latching the whole position word, and then following with the Low byte, this may be ordered from the factory at no additional cost. It is a minor PLD change in the Decoder. Another highly desirable option in real applications is to have the Status bit latched into the MSB of the High byte, along with the data. In this way, the microcontroller can easily test the data for validity, and the status may be stored with the data it relates to for post-processing. This scheme is possible for encoder systems with final resolutions up to 15 bits only.The Status bit on output pin 1 changes asynchronously, as data validity changes during initialization or upon detecting an error. It may be hard wired to an IRQ, visual indicator, etc. D0 of the Low byte is always the LSB of the complete position word. AddressData OEHOELByteBitFunction D7B15 D6B14 D5B13 01HiD0B8 D4B12 D3B11 D2B10 D1B9 D7B7 D6B6 D5B5 10LoD0B0, LSB always D4B4 D3B3 D2B2 D1B1 11Hi-ZD7-D0Data lines are tri-state 00XD7-D0Disallowed state, outputs not predictable Gurley Precision Instruments514 Fulton StreetTroy, NY 12180 U.S.A.(800) 759-1844, (518) 272-6300, fax (518) 274-0336, Online at www.gurley.com, e-mail: info@industrial encoders.com Page 3 of 7 VG GPIGPI IIIIIIIIIIIIII
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