Philips LPC2101 - UART1 Baudrate Calculation

© Koninklijke Philips Electronics N.V. 2006. All rights reserved.
User manual Rev. 01 — 12 January 2006 103
Philips Semiconductors
UM10161
Volume 1 Chapter 10: UART1
If the U1FDR register value does not comply to these two requests then the fractional
divider output is undefined. If DIVADDVAL is zero then the fractional divider is disabled
and the clock will not be divided.
The value of the U1FDR should not be modified while transmitting/receiving data or data
may be lost or corrupted.
Usage Note: For practical purposes, UART1 baudrate formula can be written in a way
that identifies the part of a UART baudrate generated without the fractional baudrate
generator, and the correction factor that this module adds:
(5)
Based on this representation, fractional baudrate generator contribution can also be
described as a prescaling with a factor of MULVAL / (MULVAL + DIVADDVAL).
10.3.5 UART1 baudrate calculation
Example 1: Using UART1baudrate formula from above, it can be determined that system
with PCLK = 20 MHz, U1DL = 130 (U1DLM = 0x00 and U1DLL = 0x82), DIVADDVAL = 0
and MULVAL = 1 will enable UART1 with UART1baudrate = 9615 bauds.
Example 2: Using UART1baudrate formula from above, it can be determined that system
with PCLK = 20 MHz, U1DL = 93 (U1DLM = 0x00 and U1DLL = 0x5D), DIVADDVAL = 2
and MULVAL = 5 will enable UART1 with UART1baudrate = 9600 bauds.
UART1
baudrate
PCLK
16 16 U1DLM× U1DLL+()×
-----------------------------------------------------------------------------
MulVal
MulVal DivAddVal+()
------------------------------------------------------------
×=
Table 104: Baudrates available when using 20 MHz peripheral clock (PCLK = 20 MHz)
Desired
baudrate
MULVAL = 0 DIVADDVAL = 0 Optimal MULVAL & DIVADDVAL
U1DLM:U1DLL % error
[3]
U1DLM:U1DLL
dec
[1]
Fractional
pre-scaler value
MULDIV
MULDIV + DIVADDVAL
% error
[3]
hex
[2]
dec
[1]
50 61A8 25000 0.0000 25000 1/(1+0) 0.0000
75 411B 16667 0.0020 12500 3/(3+1) 0.0000
110 2C64 11364 0.0032 6250 11/(11+9) 0.0000
134.5 244E 9294 0.0034 3983 3/(3+4) 0.0001
150 208D 8333 0.0040 6250 3/(3+1) 0.0000
300 1047 4167 0.0080 3125 3/(3+1) 0.0000
600 0823 2083 0.0160 1250 3/(3+2) 0.0000
1200 0412 1042 0.0320 625 3/(3+2) 0.0000
1800 02B6 694 0.0640 625 9/(9+1) 0.0000
2000 0271 625 0.0000 625 1/(1+0) 0.0000
2400 0209 521 0.0320 250 12/(12+13) 0.0000
3600 015B 347 0.0640 248 5/(5+2) 0.0064
4800 0104 260 0.1600 125 12/(12+13) 0.0000