Command Descriptions
Structure/Logic Description
The Retail VFD firmware is comprised of operating system type services such as common subroutines, interrupt service routines, and data processing routines. Normally, the firmware is always active refreshing the Retail VFD to keep display data visible. The firmware will also act on interrupts due to host parallel communication. This communication is in the form of commands from the host to the Retail VFD that require the Retail VFD to modify the display appearance.
The Retail VFD firmware uses a
Host/Retail VFD Command Interface
The Retail VFD accepts two types of data; display data and command data. If a byte received from the host is any character except ESC (0x1B) character, it is processed as a character and displayed on the Retail VFD. If an ESC character (0x1B) is received, the subsequent byte(s) is processed as a command. If the subsequent byte is an invalid command it will be ignored. If an ESC is received, but no subsequent byte is received within ten seconds, the firmware will ignore it.
Note that each command consists of at least two bytes. The first byte (0x1B) is a command identifier indicating the next byte(s) is a command byte. The command byte may be followed by parameter or data bytes depending on the command. It is only valid to receive an ESC (0x1B) as a command identifier.
The following table describes the supported Retail VFD commands.
