Communication between STMF4 and STMF1

Hi there,
Currently I want to erase code from stmf100 and send simple message to stmf4.
Is there a possibility to send a frame from STMf100 to STMF4 without changing the code on STMF4? I know that there is a uart connection, but I can’t find a method reading frames on STMF4. Is there any?
This is a packet of data to communicate:
333 struct IOPacket { 334 uint8_t count_code; 335 uint8_t crc; 336 uint8_t page; 337 uint8_t offset; 338 uint16_t regs[PKT_MAX_REGS]; 339 };
What can I send from stmF1 to get any answer?