SSI / Encoder / Quadrature Counter (Module E7)68C3 Operations Manual North Atlantic Industries, Inc. 12/19/2014Rev: 2014-12-19-0947 www.naii.com Page 275 of 330Multiple Channel ReadMulti-channel read, is used to simultaneously latch the value of two or more counter channels, or readsimultaneously the position of two or more SSI encoder channels. The Multiple Channel Read function is enabledthrough the Global Control Register. A Multiple Channel Read is triggered by writing ‘1’ to the MCRTR-bit, oralternatively by setting the ITRG bit and enabling the interval timer. When setting the ITRG bit, a Multi–Channelread cycle is triggered each time the interval timer reaches terminal count. To become part of a Multi-channelread group, the MCHRD bit(s) needs to be set ‘1’ for the associated channel.For Counter modes when using the Multiple Channel Read function, the Multi–Channel read latches the value ofthe counters that are programmed to be part for the Multi-channel read group. The latched value of counter isavailable immediately after the trigger occurs.For SSI modes a Multiple Channel Read trigger starts a conversion for the SSI channels that are part of thegroup. SSI channels need time for the conversion to complete. To indicate that the data for all the SSI channelsthat are part of the group is available, the MCRST bit in the Global Control Register is set to ’1’. The MCRSTremains set, until cleared by writing the MCRST bit with a ’1’.The Multiple Channel Read MCRST bit may also be programmed to generate an interrupt.Multi-channel read Data AvailabilitySSI ModeMCRST = ‘0’ SSI conversion is in process, or hasn’t beentriggered. New data is not available. MCRST is clearedby writing a ‘1’, to MCRST bitMCRST = ‘1’ SSI conversion for channels that are part ofthe group is completeExample: Channels 1-3 are configured for SSI mode, channels 4-6 are configured for counter mode. Channels 1,4 and 6 are enabled for Multiple Channel Read. A write to the MCRTR bit starts the Multiple Channel Read.Channel 1 starts a conversion and the counter value of channels 4 and 6 are latched. The latched counter valuefor the enabled counter channels is instantly available and can be read at once. The SSI data is not available untilMCRST is set to ’1’. The MCRST status is reset to ‘0’ by writing a “1” to MCRST bit’.Alternatively an interrupt can be set up for the SSI channel that takes the longest time to complete a conversion. Ifonly counter channels use the multi-channel function, interrupts are not necessary because the counter data isinstantly available on MCRTR trigger, or on the Interval Timer terminal count, which has an interrupt.
