SCA Functional Specification

Background

A major retail client running SCA through a third-party payment processor needed UI consistency across two POS systems during a platform migration. The legacy approach rendered screens by transmitting a large base64-encoded image payload on every single update, bandwidth-heavy, repetitive, and increasingly unreliable under high-frequency display command flows.
This feature removes that overhead by allowing the POS to reference images already stored on the terminal, sending only a short filename instead of a full binary-encoded payload. Images must be preloaded onto the terminal in advance via MSR package deployment or VHQ content management before they can be used.

Applicable Commands

The DISPLAY_IMG_TOP_NAME field is added as a new optional field to the following SCA device commands:

• Customer Question
• Quick Credit Application
• Display Message

How It Works

• The POS sends DISPLAY_IMG_TOP_NAME containing only the filename with extension of a pre-stored image.
• Images must reside at /home/usr1/flash/www/<resolution>/Images on the terminal.
• Supported image formats: PNG and JPEG / JPG.
• SCA resolves the filename at render time and displays the image as the top image on the screen.
• If both DISPLAY_IMG_TOP (base64) and DISPLAY_IMG_TOP_NAME are present in the same request, DISPLAY_IMG_TOP takes priority and DISPLAY_IMG_TOP_NAME is ignored. This ensures full backward compatibility for existing integrations.

Fallback Behaviour

If the referenced image file is not found on the terminal, the application:

• Continues processing the command without interruption.
• Renders the screen without the top image (no failure or error returned to POS).
• Logs the event, including the missing image filename.

<TRANSACTION>
        <FUNCTION_TYPE>PAYMENT</FUNCTION_TYPE>
        <COMMAND>CUST_QUESTION</COMMAND>
        <DISPLAY_IMG_TOP_NAME>store_logo.png</DISPLAY_IMG_TOP_NAME>
        <CUST_QUESTION_PROMPT>Do you want a receipt?</CUST_QUESTION_PROMPT>
</TRANSACTION>