ES-Link is an open development of YaMoRC on the s88 bus. From that also emerges the name Extended S88 bus.
Physically It enables two adjacent YaMoRC modules to be interconnected by means of the ES-Link stick: This comes in handy at the moment one e.g. wants to create a 32, 48 or larger input LocoNet feedback module by combining YD6016LN with multiple YD6016ES feedback modules.
Usually so called s88 Master modules com with one ES-Link connector: ES-IN-Link. This connector is usually present on most YaMoRC modules with a USB connection. In that case, the ES-IN-Link also provides bi-directional serial communication based on a UART protocol at 9600 Baud. This enables modules which do not have a USB connection, still to be configured and updated when connected to a module with ES-IN-Link. Such USB-less modules can have either ES-PGM-Link or ES-OUT-Link connectors. Both are Identical and must be connected to a ES-IN-Link module. Finally a module can have ES-IN-Link and as well ES-OUT-Link. Such modules can be daisy-chained and provide so called transparent mode. Examples: A 32-input LocoNet feedback module, created by combining YD6016ES and YD6016LN and the ES-Link stick. A YD8044 Decoder connected to a YD6016LN for configuration and update purposes.