National CP3BT26 - Manual (Page 166)

www.national.com 166
CP3BT26
parity bit is generated and transmitted following the eight
data bits.
Figure 80. 8-Bit Data Frame Options
The format shown in Figure 81 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 UnTBUF and UnRBUF 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.
Figure 81. 9-bit Data Frame Options
22.2.6 Baud Rate Generator
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 (UnPSC) and an 11-bit baud rate divisor (UnDIV).
The relationship between the 5-bit prescaler select (UnP-
SC) setting and the prescaler factors is shown in Table 69.
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 UnPSR register
must contain a value other than zero when an external clock
is used at CKX.
22.2.7 Interrupts
The UART is capable of generating interrupts on:
„ Receive Buffer Full
„ Receive Error
„ Transmit Buffer Empty
Table 69 Prescaler Factors
Prescaler Select Prescaler Factor
00000 No clock
00001 1
00010 1.5
00011 2
00100 2.5
00101 3
00110 3.5
00111 4
01000 4.5
01001 5
01010 5.5
2
Start
Bit 8-Bit Data 1S
2a
Start
Bit
8-Bit Data 2S
2b
Start
Bit
8-Bit Data 1S PA
2c
Start
Bit 8-Bit Data 2S PA
DS064
3
Start
Bit
9-Bit Data 1S
3a
Start
Bit
9-Bit Data 2S
DS065
01011 6
01100 6.5
01101 7
01110 7.5
01111 8
10000 8.5
10001 9
10010 9.5
10011 10
10100 10.5
10101 11
10110 11.5
10111 12
11000 12.5
11001 13
11010 13.5
11011 14
11100 14.5
11101 15
11110 15.5
11111 16
Table 69 Prescaler Factors (Continued)
Prescaler Select Prescaler Factor