R303a is working with its own protocol.
You have to read datasheet for that carefully.
When communicate with 8051, the controller has to send a command packet to the R303a fingerprint module.
After receiving command from the controller, the module send acknowledge command to the controller.
VryPwd is a command sent by controller to the module.
First two bytes are header, next four are address, next one is for package identifier, next two are for package length, next one is for instruction code, next for are for password of module, and last two are checksum.
Again I say that read the datasheet carefully.