Omron Electronics has released two cards with a SSI (Synchronous Serial Interface). The CS1W-CTS21 and CJ1W-CTS21 work on the CS1 and CJ1 series, respectively. Both cards support two input channels, with the CS1 unit supporting an additional four inputs and outputs.
Although SSI is a relatively new interface, it is beginning to be more commonplace in the market. SSI is used in applications where high-speed pulse trains need to be transmitted over a significant distance in an electrically noisy environment. The common usage is for high-resolution rotary encoders, operating at high-speed. The CTS21 units support both BCD and grey code encoders.
SSI achieves long transmission distances by using a synchronous signal, with a separate clock pulse. Both signals have a separate ground terminal, rather than a shared one. Power for the encoder can also be supplied via the CTS21 card. The clock speed can be set between 100KHz to 1.5Mhz, achieving transmission distances of between 50 and 400M.