SB16C1052PCI_Data Sheet_EN

SB16C1052PCI
PCI Target Interface Controller
with Dual UART
JULY 2013 REV 1.06
39
12.3 Software Flow Control
Software flow control is performed by Xon and Xoff character transmitting/accepting.
Software flow control is enabled/disabled independently by programming EFR[3:0]
and MCR[6:5, 2]. If TX software flow control is enabled by EFR[3:2], Xoff character is
transmitted to report that data can not be accepted when the stored amount of data in
RX FIFO exceeds the value in FUR. After the CPU reads the data in RX FIFO and if
the read amount is less than the value in FLR, Xon character is transmitted to report
that more data can be accepted. If TX software flow control is enabled by EFR[1:0]
and Xoff character is inputted through RXD pin, it means no more data can be
accepted, and data transmission is suspended even though data are in TX FIFO. If
Xon character is received through RXD pin while data transmission is suspended, it
means more data can be accepted, and therefore data in TX FIFO are re-transmitted.
These procedures prevent overruns during communication. If software flow control is
disabled, overrun occurs when the transmit data rate exceeds RX FIFO service
latency. Different combinations of software flow control can be enabled by setting
different combinations of EFR[3:0] . Table 12–1 shows software flow control options.
Table 12–1: Software flow control options (EFR[3:0])
EFR[3]
EFR[2]
EFR[1]
EFR[0]
TX, RX software flow controls
0
0
X
X
No transmit control
1
0
X
X
Transmit Xon1/Xoff1
0
1
X
X
Transmit Xon2/Xoff2
1
1
X
X
Transmit Xon1, Xon2/Xoff1, Xoff2
X
X
0
0
No receive flow control
X
X
1
0
Receiver compares Xon1/Xoff1
X
X
0
1
Receiver compares Xon2/Xoff2
X
X
1
1
Receiver compares Xon1, Xon2/Xoff1, Xoff2
0
0
0
0
No transmit control, No receive flow control
0
0
1
0
No transmit control, Receiver compares Xon1/Xoff1
0
0
0
1
No transmit control, Receiver compares Xon2/Xoff2
0
0
1
1
No transmit control, Receiver compares Xon1, Xon2/Xoff1, Xoff2
1
0
0
0
Transmit Xon1/Xoff1, No receive flow control
1
0
1
0
Transmit Xon1/Xoff1, Receiver compares Xon1/Xoff1
1
0
0
1
Transmit Xon1/Xoff1, Receiver compares Xon2/Xoff2
1
0
1
1
Transmit Xon1/Xoff1, Receiver compares Xon1, Xon2/Xoff1, Xoff2
0
1
0
0
Transmit Xon2/Xoff2, No receive flow control
0
1
1
0
Transmit Xon2/Xoff2, Receiver compares Xon1/Xoff1
0
1
0
1
Transmit Xon2/Xoff2, Receiver compares Xon2/Xoff2
0
1
1
1
Transmit Xon2/Xoff2, Receiver compares Xon1, Xon2/Xoff1, Xoff2
1
1
0
0
Transmit Xon2/Xoff2, No receive flow control
1
1
1
0
Transmit Xon2/Xoff2, Xoff2, Receiver compares Xon1/Xoff1
1
1
0
1
Transmit Xon1, Xon2/Xoff1, Xoff2, Receiver compares Xon2/Xoff2
1
1
1
1
Transmit Xon1, Xon2/Xoff1, Xoff2, Receiver compares Xon1, Xon2/Xoff1, Xoff2