SC16C852V All information provided in this document is subject to legal disclaimers. © NXP B.V. 2011. All rights reserved.
Product data sheet Rev. 5 — 21 January 2011 13 of 55
NXP Semiconductors
SC16C852V
Dual UART with 128-byte FIFOs, IrDA, and XScale VLIO bus interface
In the event that the receive buffer is overfilling, the SC16C852V automatically sends an
Xoff character (when enabled) via the serial TX output to the remote UART. The
SC16C852V sends the Xoff1/Xoff2 characters as soon as the number of received data in
the receive FIFO passes the programmed trigger level. To clear this condition, the
SC16C852V will transmit the programmed Xon1/Xon2 characters as soon as the number
of characters in the receive FIFO drops below the programmed trigger level.
6.7 Special character detect
A special character detect feature is provided to detect an 8-bit character when EFR[5] is
set. When an 8-bit character is detected, it will be placed on the user-accessible data
stack along with normal incoming RXA/RXB data. This condition is selected in conjunction
with EFR[3:0] (see Table 26
). Note that software flow control should be turned off when
using this special mode by setting EFR[3:0] to all zeroes.
The SC16C852V compares each incoming receive character with Xoff2 data. If a match
occurs, the received data will be transferred to the FIFO, and ISR[4] will be set to indicate
detection of a special character. Although Table 9 “
SC16C852V internal registers” shows
Xon-1, Xon-2, Xoff-1, Xoff-2 with eight bits of character information, the actual number of
bits is dependent on the programmed word length. Line Control Register bits LCR[1:0]
define the number of character bits, that is, either 5bits, 6bits, 7bits or 8bits. The word
length selected by LCR[1:0] also determine the number of bits that will be used for the
special character comparison. Bit 0 in the Xon-1, Xon-2, Xoff-1, Xoff-2 registers
corresponds with the LSB bit for the received character.
6.8 Interrupt priority and time-out interrupts
The interrupts are enabled by IER[7:0]. Care must be taken when handling these
interrupts. Following a reset, if Interrupt Enable Register (IER) bit 1 = 1, the SC16C852V
will issue a Transmit Holding Register interrupt. This interrupt must be serviced prior to
continuing operations. The ISR indicates the current singular highest priority interrupt
only. A condition can exist where a higher priority interrupt masks the lower priority
interrupt(s) (see Table 14
). Only after servicing the higher pending interrupt will the lower
priority interrupt(s) be reflected in the status register. Servicing the interrupt without
investigating further interrupt conditions can result in data errors.
Receive Data Ready and Receive Time Out have the same interrupt priority (when
enabled by IER[0]), and it is important to serve these interrupts correctly. The receiver
issues an interrupt after the number of characters have reached the programmed trigger
level. In this case, the SC16C852V FIFO may hold more characters than the programmed
trigger level. Following the removal of a data byte, the user should re-check LSR[0] to see
if there are any additional characters. A Receive Time Out will not occur if the receive
FIFO is empty. The time-out counter is reset at the center of each stop bit received or
each time the Receive Holding Register (RHR) is read. The actual time-out value is
4 character time, including data information length, start bit, parity bit, and the size of stop
bit, that is, 1×, 1.5×, or 2× bit times.
