pc87591l-n05 National Semiconductor Corporation, pc87591l-n05 Datasheet - Page 151

• Manufacturer Part Number: pc87591l-n05
• Description: Lpc Mobile Embedded Controller
• Manufacturer: National Semiconductor Corporation

Revision 1.2
4.0 Embedded Controller Modules
The format shown in Figure 55 consists of one start bit, eight data bits (excluding parity) and one or two stop bits. If parity
bit generation is enabled by setting the PEN bit, a parity bit is generated and transmitted following the eight data bits.
The format shown in Figure 56 consists of one start bit, nine data bits and one or two stop bits. This format also supports
the USART 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 STPXB9 and RB9. Parity is not gen-
erated or verified in this mode.
Baud Rate Generator
The Baud Rate Generator provides 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 pre-scaler (PSC) and an 11-bit baud rate divisor (DIV).
The correspondences between the 5-bit pre-scaler select (PSC) and pre-scaler factors are shown in Table 20.
A pre-scaler factor of zero corresponds to NO CLOCK. The NO CLOCK condition is the USART Power-Down mode. In this
mode, the USART clock is turned off in order to reduce power consumption. The user should set the pre-scaler factor to zero
(NO CLOCK) before selecting a new baud rate. Altering the baud rate while the USART is in operation could cause incorrect
data to be received or transmitted. UnPSR register must contain a value other than zero when an external clock is used at
USCLKn.
In Asynchronous mode, the baud rate is calculated by:
BR = SYS_CLK/(16 x N x P)
2a
2b
2c
3a
2
3
1
1a
1b
1c
START
START
START
START
START
START
BIT
BIT
BIT
BIT
BIT
BIT
START
START
START
START
BIT
BIT
BIT
BIT
Figure 54. Seven Data Bit Frame Options
Figure 55. Eight Data Bit Frame Options
Figure 56. Nine Data Bit Frame Options
8-BIT DATA
(Continued)
7-BIT DATA
8-BIT DATA
8-BIT DATA
8-BIT DATA
9-BIT DATA
9-BIT DATA
7-BIT DATA
7-BIT DATA
7-BIT DATA
151
PA
PA
S
PA
2S
PA
S
S
2S
2S
S
S
2S
2S
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