Resolved! 7 USART3 registers == 28 bytes. What are the other addresses in USART3 for?
STM32F407 Discovery typedef struct __UART_HandleTypeDef { USART_TypeDef *Instance; UART_InitTypeDef Init; const uint8_t *pTxBuffPtr; uint16_t TxXferSize; __IO uint16_t TxXferCount; uint8_t *pRxBuffPtr; uint16_t RxXferSize; __IO uint16_t RxXferCount;...