C8051F50x-F51x
Use the following equations to calculate the values for the variables for the baud-rate equation:
20000
multiplier = ----------------------------- – 1
baud_rate
SYSCLK
1
ln2
------------------------------------------------------------------------------------------------
prescaler = ln
-------- – 1
multiplier + 1 baud_rate 200
SYSCLK
divider = -------------------------------------------------------------------------------------------------------------------------------------
prescaler + 1
2
multiplier + 1 baud_rate
In all of these equations, the results must be rounded down to the nearest integer.
The following example shows the steps for calculating the baud rate values for a Master node running at
24 MHz and communicating at 19200 bits/sec. First, calculate the multiplier:
20000
multiplier = ---------------- – 1 = 0. 0417 0
19200
Next, calculate the prescaler:
24000000
1
ln2
-----------------------------------------------------------
prescaler = ln
-------- – 1 = 1.644 1
0 + 1 19200 200
Finally, calculate the divider:
24000000
divider = ---------------------------------------------------------------------- = 312.5 312
1 + 1
2
0 + 1 19200
These values lead to the following baud rate:
24000000
----------------------------------------------------------------
2
baud_rate =
19230.77
1 + 1
0 + 1 312
The following code programs the interface in Master mode, using the Enhanced Checksum and enables
the interface to operate at 19230 bits/sec using a 24 MHz system clock.
LIN0CF
LIN0CF |= 0x40;
= 0x80;
// Activate the interface
// Set the node as a Master
LIN0ADR = 0x0D;
// Point to the LIN0MUL register
// Initialize the register (prescaler, multiplier and bit 8 of divider)
LIN0DAT = ( 0x01 << 6 ) + ( 0x00 << 1 ) + ( ( 0x138 & 0x0100 ) >> 8 );
LIN0ADR
LIN0DAT
= 0x0C;
= (unsigned char)_0x138;
// Point to the LIN0DIV register
// Initialize LIN0DIV
LIN0ADR
= 0x0B;
// Point to the LIN0SIZE register
LIN0DAT |= 0x80;
// Initialize the checksum as Enhanced
LIN0ADR
LIN0DAT
= 0x08;
= 0x0C;
// Point to LIN0CTRL register
// Reset any error and the interrupt
Rev. 1.1
203
SILICON [ SILICON ]
