Cirrus Logic ARM CDB89712, User Manual

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CDB89712
6-2 DS502UM2
6.3.1.1. UART0 (J8)
The primary serial port of the CS89712 is UART0. This UART contains many of the standard
modem control signals found in a standard UART. The signals not implemented by the CS89712 are
DTR, RTS and RI. The development board implements both RTS and RI through GPIO pins. The
definition is given in
Table 6-2 below.
The UART0 signals are converted to and from RS-232 levels by a single device (U13). The DTR
signal is driven high or low through jumper JP36. This is done to support serial mice that require all
transmitter signals are driven to either a positive or negative voltage. DTR is normally pulled up; it
can be pulled down by installing jumper JP36.
6.3.1.2. UART1 (J9)
UART1 is a simplified serial port in the sense that none of the extra control signals are present, only
RXD and TXD. This port is driven as with Serial Port 0, using a serial port voltage level shifter. This
port has the added feature that the serial port voltage level shifter may be disabled, and the
CS89712’s driver pins are accessed directly. This is accomplished by installing a jumper on JP35,
and using JP34 to access the port pins. JP34 is outlined in
Table 6-3 below.
6.3.1.3. Controlling Serial Port Communications
Table 6-4 describes the jumper setting for enabling / disabling COM1 and COM2 communications
and for setting the COM1 DTR signal high or low.
Serial Port 0 Signal GPIO Pin
RTS PB1
RI PB2
Table 6-2. Serial Port GPIO Implemented Connections
Pin # Name
1 TXD2
2 RXD2
3 Ground
Table 6-3. Serial Port Logic Level Header (JP34)
Jumper Name Description
JP35 COM2
ENABLE /
DISABLE Enabled. (Factory setting)
Disabled. Notice that this only affects the
driver IC, and will not disable the port in the
CS89712 itself. The intent of this jumper is to
permit use of logic level RS232
communications via JP34.
JP36 COM1 DTR
HIGH / LOW DTR set high. This should be used for most
applications. (Factory setting)
DTR set low. Used to disable
communications, or when DTR is negative
true.
Table 6-4. Serial Port Control Jumper Assignments