cp3cn17 National Semiconductor Corporation, cp3cn17 Datasheet - Page 125

• Manufacturer Part Number: cp3cn17
• Description: Reprogrammable Connectivity Processor With Can Interface
• Manufacturer: National Semiconductor Corporation

parity bit is generated and transmitted following the eight
data bits.
The format shown in Figure 59 consists of one start bit, nine
data bits, and one or two stop bits. This format also supports
the UART attention feature. When operating in this format,
all eight bits of UTBUF and URBUF are used for data. The
ninth data bit is transmitted and received using two bits in
the control registers, called UXB9 and URB9. Parity is not
generated or verified in this mode.
18.2.6
The Baud Rate Generator creates the basic baud clock from
the System Clock. The System Clock is passed through a
two-stage divider chain consisting of a 5-bit baud rate pres-
caler (UPSC) and an 11-bit baud rate divisor (UDIV).
The relationship between the 5-bit prescaler select (UPSC)
setting and the prescaler factors is shown in Table 56.
2a
2b
2c
3a
2
3
Prescaler Select
Baud Rate Generator
Figure 58. 8-Bit Data Frame Options
Figure 59. 9-bit Data Frame Options
Start
Start
Start
Start
Start
Start
Bit
Bit
Bit
Bit
Bit
Bit
00000
00001
00010
00011
00100
00101
00110
00111
01000
01001
01010
Table 56 Prescaler Factors
8-Bit Data
8-Bit Data
8-Bit Data
8-Bit Data
9-Bit Data
9-Bit Data
Prescaler Factor
No clock
PA
1S
PA
1.5
2.5
3.5
4.5
5.5
2S
1
2
3
4
5
1S
1S
2S
2S
DS064
DS065
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A prescaler factor of zero corresponds to “no clock.” The “no
clock” condition is the UART power down mode, in which the
UART clock is turned off to reduce power consumption.
Software must select the “no clock” condition before enter-
ing a new baud rate. Otherwise, it could cause incorrect
data to be received or transmitted. The UPSR register must
contain a value other than zero when an external clock is
used at CKX.
18.2.7
The UART is capable of generating interrupts on:
Receive Buffer Full
Receive Error
Transmit Buffer Empty
Prescaler Select
Table 56 Prescaler Factors (Continued)
Interrupts
01011
01100
01101
01110
01111
10000
10001
10010
10011
10100
10101
10110
10111
11000
11001
11010
11011
11100
11101
11110
11111
Prescaler Factor
10.5
11.5
12.5
13.5
14.5
15.5
6.5
7.5
8.5
9.5
10
11
12
13
14
15
16
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