DRAFT
DRAFT DRAFT DR
DRAFT DRAFT DRAFT
D
RAF
DRAFT DRAFT DRA
FT D
RAFT DR
AFT D
DRA
FT DRAFT DRAFT
D
RAFT
DRAFT
D
RAFT
DRA
UM10601
All information provided in this document is subject to legal disclaimers.
© NXP B.V. 2012. All rights reserved.
Preliminary user manual
Rev. 1.0 — 7 November 2012
180 of 313
NXP Semiconductors
UM10601
Chapter 15: LPC800 USART0/1/2
15.7 Functional description
15.7.1 Clocking and Baud rates
In order to use the USART, clocking details must be defined such as setting up the BRG,
and typically also setting up the FRG. See
15.7.1.1 Fractional Rate Generator (FRG)
The Fractional Rate Generator can be used to obtain more precise baud rates when the
peripheral clock is not a good multiple of standard (or otherwise desirable) baud rates.
The FRG is typically set up to produce an integer multiple of the highest required baud
rate, or a very close approximation. The BRG is then used to obtain the actual baud rate
needed.
The FRG register controls the USART Fractional Rate Generator, which provides the
base clock for the USART. The Fractional Rate Generator creates a lower rate output
clock by suppressing selected input clocks. When not needed, the value of 0 can be set
for the FRG, which will then not divide the input clock.
The FRG output clock is defined as the inputs clock divided by 1 + (MULT / 256), where
MUTL is in the range of 1 to 255. This allows producing an output clock that ranges from
the input clock divided by 1+1/256 to 1+255/256 (just more than 1 to just less than 2). Any
further division can be done specific to each USART block by the integer BRG divider
contained in each USART.
4:3
-
Reserved. Read value is undefined, only zero should be
written.
NA
5
DELTACTS
This bit is set when a change in the state of the CTS input is
detected.
0
6
TXDISINT
Transmitter Disabled Interrupt flag.
0
7
-
Reserved. Read value is undefined, only zero should be
written.
NA
8
OVERRUNINT
Overrun Error interrupt flag.
0
10:9
-
Reserved. Read value is undefined, only zero should be
written.
NA
11
DELTARXBRK
This bit is set when a change in the state of receiver break
detection occurs.
0
12
START
This bit is set when a start is detected on the receiver input.
0
13
FRAMERRINT
Framing Error interrupt flag.
0
14
PARITYERRINT
Parity Error interrupt flag.
0
15
RXNOISEINT
Received Noise interrupt flag.
0
31:16 -
Reserved. Read value is undefined, only zero should be
written.
NA
Table 167. USART Interrupt Status register (INTSTAT, address 0x4006 4024 (USART0),
0x4006 8024 (USART1), 0x4006 C024(USART2)) bit description
Bit
Symbol
Description
Reset
Value