UM10503
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User manual
Rev. 1.3 — 6 July 2012
999 of 1269
NXP Semiconductors
UM10503
Chapter 38: LPC43xx UART1
38.6.16 UART1 RS-485 Address Match register
The RS485ADRMATCH register contains the address match value for RS-485/EIA-485
mode.
38.6.17 UART1 RS-485 Delay value register
The user may program the 8-bit RS485DLY register with a delay between the last stop bit
leaving the TXFIFO and the de-assertion of RTS (or DTR). This delay time is in periods of
the baud clock. Any delay time from 0 to 255 bit times may be programmed.
38.7 Functional description
38.7.1 Auto-flow control
If auto-RTS mode is enabled the UART1‘s receiver FIFO hardware controls the RTS1
output of the UART1. If the auto-CTS mode is enabled the UART1‘s TSR hardware will
only start transmitting if the CTS1 input signal is asserted.
38.7.1.1
Auto-RTS
The auto-RTS function is enabled by setting the RTSen bit. Auto-RTS data flow control
originates in the RBR module and is linked to the programmed receiver FIFO trigger level.
If auto-RTS is enabled, the data-flow is controlled as follows:
When the receiver FIFO level reaches the programmed trigger level, RTS1 is de-asserted
(to a high value). It is possible that the sending UART sends an additional byte after the
trigger level is reached (assuming the sending UART has another byte to send) because it
might not recognize the de-assertion of RTS1 until after it has begun sending the
additional byte. RTS1 is automatically reasserted (to a low value) once the receiver FIFO
has reached the previous trigger level. The re-assertion of RTS1 signals to the sending
UART to continue transmitting data.
If Auto-RTS mode is disabled, the RTSen bit controls the RTS1 output of the UART1. If
Auto-RTS mode is enabled, hardware controls the RTS1 output, and the actual value of
RTS1 will be copied in the RTS Control bit of the UART1. As long as Auto-RTS is enabled,
the value of the RTS Control bit is read-only for software.
Table 866. UART1 RS485 Address Match register (RS485ADRMATCH - address 0x4008 2050) bit description
Bit
Symbol
Description
Reset value
7:0
ADRMATCH
Contains the address match value.
0x00
31:8
-
Reserved, user software should not write ones to reserved bits. The value read from a
reserved bit is not defined.
NA
Table 867. UART1 RS485 Delay value register (RS485DLY - address 0x4008 2054) bit description
Bit
Symbol
Description
Reset value
7:0
DLY
Contains the direction control (RTS or DTR) delay value. This register works in
conjunction with an 8-bit counter.
0x00
31:8
-
Reserved, user software should not write ones to reserved bits. The value read from a
reserved bit is not defined.
NA