Visible to Intel only — GUID: iga1404408596694
Ixiasoft
Visible to Intel only — GUID: iga1404408596694
Ixiasoft
10.2.11. Hardware Auto Flow-Control
Hardware based auto flow-control uses 2 signals (cts_n & rts_n) from the Modem Control/Status group. With Hardware auto flow-control disabled, these signals will directly drive the Modem Status register (cts_n) or be driven by the Modem Control register (rts_n).
With auto flow-control enabled, these signals perform flow-control duty with another UART at the other end.
The cts_n input is, when active (low state), will allow the Tx FIFO to send data to the transmit buffer. When cts_n is inactive (high state), the Tx FIFO stops sending data to the transmit buffer. cts_n is expected to be connected to the rts_n output of the other UART.
The rts_n output will go active (low state), when the Rx FIFO is empty, signaling to the opposite UART that it is ready for data. The rts_n output goes inactive (high state) when the Rx FIFO level is reached, signaling to the opposite UART that the FIFO is about to go full and it should stop transmitting.
Due to the delays within the UART logic, one additional character may be transmitted after cts_n is sampled active low. For the same reason, the Rx FIFO will accommodate up to 1 additional character after asserting rts_n (this is allowed because Rx FIFO trigger level is at worst, two entries from being truly full). Both are observed to prevent overflow/underflow between UARTs.