User manual

6 OnRISC Hardware API

6.4. Serial Interfaces

6.4.1. KS8695 based Devices

RS232/422/485 mode switching The serial ports can operate in one of the three modes RS232,

RS422 or RS485

(see Hardware Manual for electrical conﬁguration issues). These modes will

be controlled through the EPLD circuit. Following IOCTLS are to be used to switch the modes

(alternative /proc/vscom/epld_ttySx entries can be used to switch RS modes. See Section 7):

• TIOCGEPLD - get EPLD mode

• TIOCSEPLD - set EPLD mode

These commands use the following structure to store the desired parameters:

struct e pl d _s t ru c t

{

unsigned long po rt ;

unsigned long r e g _ s h i f t ;

unsigned long va lue ;

} ;

The ﬁeld value can have one of the following values:

• EPLD_RS232 - RS232 mode

• EPLD_RS422 - RS422 mode

• EPLD_RS485_ART_4W - RS485 mode 4-wire transmit control by ART

• EPLD_RS485_ART_2W - RS485 mode 2-wire direction control by ART

• EPLD_RS485_ART_ECHO - RS485 mode 2-wire direction control by ART with echo

• EPLD_RS485_RTS_4W - RS485 mode 4-wire transmit control by RTS

• EPLD_RS485_RTS_2W - RS485 mode 2-wire direction control by RTS

• EPLD_RS485_RTS_ECHO - RS485 mode 2-wire direction control by RTS with echo

• EPLD_CAN - CAN mode

• EPLD_PORTOFF - shutdown the port

RS485 transmission control In RS485 the line driver for transmitting must be disabled (tri-

stated) when the device does not send data. In a 2-wire conﬁguration this is known as data

direction change, with 4-wire it is called line contention. The following modes are provided by

OnRISC:

• RTS: if this mode is set user software is responsible to turn transmitter on/oﬀ by toggling

the RTS signal (RTS 1 turns sender on, RTS 0 turns sender oﬀ)

• ART (Automatic Receive Transmit): The sender will be automatically turned on/oﬀ by

hardware. The turning oﬀ occurs after the stop bit was sent (recommended mode).

See include/asm/arch/serial.h to see what EPLD capabilities each port has

May 2014 OnRISC User Manual 42