PCM18XT0 Microchip Technology, PCM18XT0 Datasheet - Page 233

• Manufacturer Part Number: PCM18XT0
• Description: MODULE PROC PIC18F4685
• Manufacturer: Microchip Technology

Specifications of PCM18XT0

• Accessory Type: Processor Module
• Product: Microcontroller Modules
• Core Processor: PIC18F4685
• Lead Free Status / RoHS Status: Not applicable / Not applicable
• For Use With/related Products: ICE2000
• For Use With: ICE2000 - EMULATOR MPLAB-ICE 2000 POD
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant, Not applicable / Not applicable

18.1
The BRG is a dedicated 8-bit or 16-bit generator that
supports both the Asynchronous and Synchronous
modes of the EUSART. By default, the BRG operates
in 8-bit mode; setting the BRG16 bit (BAUDCON<3>)
selects 16-bit mode.
The SPBRGH:SPBRG register pair controls the period
of a free-running timer. In Asynchronous mode, bits
BRGH (TXSTA<2>) and BRG16 (BAUDCON<3>) also
control the baud rate. In Synchronous mode, BRGH is
ignored. Table 18-1 shows the formula for computation
of the baud rate for different EUSART modes which
only apply in Master mode (internally generated clock).
Given the desired baud rate and F
integer value for the SPBRGH:SPBRG registers can be
calculated using the formulas in Table 18-1. From this,
the error in baud rate can be determined. An example
calculation is shown in Example 18-1. Typical baud rates
and error values for the various Asynchronous modes
are shown in Table 18-2. It may be advantageous to use
TABLE 18-1:
EXAMPLE 18-1:
TABLE 18-2:
© 2009 Microchip Technology Inc.
Legend: x = Don’t care, n = value of SPBRGH:SPBRG register pair
TXSTA
RCSTA
BAUDCON
SPBRGH
SPBRG
Legend: — = unimplemented, read as ‘0’. Shaded cells are not used by the BRG.
For a device with F
Desired Baud Rate
Solving for SPBRGH:SPBRG:
Calculated Baud Rate
Error
Name
SYNC
0
0
0
0
1
1
Baud Rate Generator (BRG)
Configuration Bits
EUSART Baud Rate Generator Register High Byte
EUSART Baud Rate Generator Register Low Byte
ABDOVF
CSRC
SPEN
Bit 7
BAUD RATE FORMULAS
BRG16
X
REGISTERS ASSOCIATED WITH BAUD RATE GENERATOR
OSC
0
0
1
1
0
1
CALCULATING BAUD RATE ERROR
of 16 MHz, desired baud rate of 9600, Asynchronous mode, 8-bit BRG:
= F
= ((F
= ((16000000/9600)/64) – 1
= [25.042] = 25
= 16000000/(64 (25 + 1))
= 9615
= (Calculated Baud Rate – Desired Baud Rate)/Desired Baud Rate
= (9615 – 9600)/9600 = 0.16%
RCIDL
Bit 6
RX9
TX9
OSC
OSC
/(64 ([SPBRGH:SPBRG] + 1)
BRGH
/Desired Baud Rate)/64) – 1
0
1
0
1
x
x
OSC
SREN
TXEN
Bit 5
—
, the nearest
PIC18F2682/2685/4682/4685
CREN
SYNC
SCKP
Bit 4
BRG/EUSART Mode
16-bit/Asynchronous
16-bit/Asynchronous
16-bit/Synchronous
8-bit/Asynchronous
8-bit/Asynchronous
8-bit/Synchronous
SENDB
ADDEN
BRG16
Bit 3
the high baud rate (BRGH = 1) or the 16-bit BRG to
reduce the baud rate error, or achieve a slow baud rate
for a fast oscillator frequency.
Writing a new value to the SPBRGH:SPBRG registers
causes the BRG timer to be reset (or cleared). This
ensures that the BRG does not wait for a timer overflow
before outputting the new baud rate.
18.1.1
The device clock is used to generate the desired baud
rate. When one of the power-managed modes is
entered, the new clock source may be operating at a
different frequency. This may require an adjustment to
the value in the SPBRG register pair.
18.1.2
The data on the RX pin is sampled three times by a
majority detect circuit to determine if a high or a low
level is present at the RX pin.
BRGH
FERR
Bit 2
—
OPERATION IN POWER-MANAGED
MODES
SAMPLING
OERR
TRMT
WUE
Bit 1
Baud Rate Formula
F
F
F
OSC
OSC
ABDEN
OSC
RX9D
TX9D
Bit 0
/[64 (n + 1)]
/[16 (n + 1)]
/[4 (n + 1)]
DS39761C-page 233
Reset Values
on page
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