SC16IS752_SC16IS762 All information provided in this document is subject to legal disclaimers. © NXP B.V. 2012. All rights reserved.
Product data sheet Rev. 9 — 22 March 2012 10 of 60
NXP Semiconductors
SC16IS752; SC16IS762
Dual UART with I
2
C-bus/SPI interface, 64-byte FIFOs, IrDA SIR
7.2.2 Auto-CTS
Figure 6 shows CTS functional timing. The transmitter circuitry checks CTS before
sending the next data character. When CTS
is active, the transmitter sends the next
character. To stop the transmitter from sending the following character, CTS
must be
de-asserted before the middle of the last stop bit that is currently being sent. The
Auto-CTS
function reduces interrupts to the host system. When flow control is enabled,
CTS
level changes do not trigger host interrupts because the device automatically
controls its own transmitter. Without Auto-CTS
, the transmitter sends any data present in
the transmit FIFO and a receiver overrun error may result.
7.3 Software flow control
Software flow control is enabled through the Enhanced Features Register and the Modem
Control Register. Different combinations of software flow control can be enabled by setting
different combinations of EFR[3:0]. Table 3
shows software flow control options.
(1) When CTS is LOW, the transmitter keeps sending serial data out.
(2) When CTS
goes HIGH before the middle of the last stop bit of the current character, the transmitter finishes sending the current
character, but it does not send the next character.
(3) When CTS
goes from HIGH to LOW, the transmitter begins sending data again.
Fig 6. CTS functional timing
start bit 0 to bit 7 stopTX
CTS
002aab041
start stop
bit 0 to bit 7
Table 3. Software flow control options (EFR[3:0])
EFR[3] EFR[2] EFR[1] EFR[0] TX, RX software flow control
0 0 X X no transmit flow control
1 0 X X transmit Xon1, Xoff1
0 1 X X transmit Xon2, Xoff2
1 1 X X transmit Xon1 and Xon2, Xoff1 and 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
1011transmit Xon1, Xoff1
receiver compares Xon1 or Xon2, Xoff1 or Xoff2
0111transmit Xon2, Xoff2
receiver compares Xon1 or Xon2, Xoff1 or Xoff2
1111transmit Xon1 and Xon2, Xoff1 and Xoff2
receiver compares Xon1 and Xon2, Xoff1 and Xoff2
0011no transmit flow control
receiver compares Xon1 and Xon2, Xoff1 and Xoff2
