PIC16F690-E/P Microchip Technology Inc., PIC16F690-E/P Datasheet - Page 167

• Manufacturer Part Number: PIC16F690-E/P
• Description: 20 PIN, 7 KB FLASH, 256 RAM, 18 I/O
• Manufacturer: Microchip Technology Inc.

Specifications of PIC16F690-E/P

• A/d Inputs: 12-Channel, 10-Bit
• Comparators: 2
• Cpu Speed: 7 MIPS
• Eeprom Memory: 256 Bytes
• Input Output: 18
• Interface: USART
• Memory Type: Flash
• Number Of Bits: 8
• Package Type: 20-pin PDIP
• Programmable Memory: 7K Bytes
• Ram Size: 256 Bytes
• Speed: 20 MHz
• Timers: 2-8-bit, 1-16-bit
• Voltage, Range: 2-5.5 V
• Lead Free Status / Rohs Status: RoHS Compliant part Electrostatic Device

12.3.1
The EUSART module supports automatic detection
and calibration of the baud rate.
In the Auto-Baud Detect (ABD) mode, the clock to the
BRG is reversed. Rather than the BRG clocking the
incoming RX signal, the RX signal is timing the BRG.
The Baud Rate Generator is used to time the period of
a received 55h (ASCII “U”) which is the Sync character
for the LIN bus. The unique feature of this character is
that it has five rising edges including the Stop bit edge.
Setting the ABDEN bit of the BAUDCTL register starts
the auto-baud calibration sequence (Figure 12-6).
While the ABD sequence takes place, the EUSART
state machine is held in Idle. On the first rising edge of
the receive line, after the Start bit, the SPBRG begins
counting up using the BRG counter clock as shown in
Table 12-6. The fifth rising edge will occur on the RX
pin at the end of the eighth bit period. At that time, an
accumulated value totaling the proper BRG period is
left in the SPBRGH, SPBRG register pair, the ABDEN
bit is automatically cleared and the RCIF interrupt flag
is set. The value in the RCREG needs to be read to
clear the RCIF interrupt. RCREG content should be
discarded. When calibrating for modes that do not use
the SPBRGH register the user can verify that the
SPBRG register did not overflow by checking for 00h in
the SPBRGH register.
The BRG auto-baud clock is determined by the BRG16
and BRGH bits as shown in Table 12-6. During ABD,
both the SPBRGH and SPBRG registers are used as a
16-bit counter, independent of the BRG16 bit setting.
While calibrating the baud rate period, the SPBRGH
FIGURE 12-6:
© 2006 Microchip Technology Inc.
BRG Value
BRG Clock
ABDEN bit
RCIF bit
(Interrupt)
SPBRGH
RCREG
SPBRG
RX pin
RCIDL
Note 1:
Read
AUTO-BAUD DETECT
Set by User
The ABD sequence requires the EUSART module to be configured in Asynchronous mode.
XXXXh
AUTOMATIC BAUD RATE CALIBRATION
0000h
PIC16F631/677/685/687/689/690
Start
bit 0
XXh
XXh
Edge #1
Preliminary
bit 1
bit 2
Edge #2
and SPBRG registers are clocked at 1/8th the BRG
base clock rate. The resulting byte measurement is the
average bit time when clocked at full speed.
TABLE 12-6:
BRG16
Note:
Note 1: If the WUE bit is set with the ABDEN bit,
bit 3
0
0
1
1
2: It is up to the user to determine that the
3: During the auto-baud process, the
bit 4
Edge #3
BRGH
During the ABD sequence, SPBRG and
SPBRGH registers are both used as a 16-bit
counter, independent of BRG16 setting.
auto-baud detection will occur on the byte
following the Break character (see
Section 12.3.2
Break”).
incoming character baud rate is within the
range of the selected BRG clock source.
Some combinations of oscillator frequency
and EUSART baud rates are not possible.
auto-baud counter starts counting at 1.
Upon
sequence,
accuracy,
SPBRGH:SPBRG register pair.
0
1
0
1
bit 5
BRG COUNTER CLOCK RATES
completion
bit 6
BRG Base
Edge #4
F
F
F
F
Clock
OSC
OSC
OSC
subtract
OSC
to
bit 7
/64
/16
/16
/4
“Auto-Wake-up
achieve
of
DS41262C-page 165
Stop bit
Edge #5
1
the
Auto Cleared
BRG ABD
001Ch
F
F
F
F
1Ch
00h
OSC
OSC
OSC
from
Clock
OSC
auto-baud
maximum
/512
/128
/128
/32
the
on