SC16IS762 Philips Semiconductors, SC16IS762 Datasheet - Page 34

• Manufacturer Part Number: SC16IS762
• Description: (SC16IS752 / SC16IS762) Dual UART
• Manufacturer: Philips Semiconductors

NXP Semiconductors
SC16IS752_SC16IS762_6
Product data sheet
9.3.1 Normal multidrop mode
9.3.2 Auto address detection
9.3 Auto RS-485
EFCR bit 0 is used to enable the RS-485 mode (multidrop or 9-bit mode). In this mode of
operation, a ‘master’ station transmits an address character followed by data characters
for the addressed ‘slave’ stations. The slave stations examine the received data and
interrupt the controller if the received character is an address character (parity bit = 1).
To use the auto RS-485 RTS mode the software would have to disable the hardware flow
control function.
The 9-bit mode in EFCR (bit 0) is enabled, but not Special Character Detect (EFR bit 5).
The receiver is set to Force Parity 0 (LCR[5:3] = 111) in order to detect address bytes.
With the receiver initially disabled, it ignores all the data bytes (parity bit = 0) until an
address byte is received (parity bit = 1). This address byte will cause the UART to set the
parity error. The UART will generate a line status interrupt (IER bit 2 must be set to ‘1’ at
this time), and at the same time puts this address byte in the RX FIFO. After the controller
examines the byte it must make a decision whether or not to enable the receiver; it should
enable the receiver if the address byte addresses its ID address, and must not enable the
receiver if the address byte does not address its ID address.
If the controller enables the receiver, the receiver will receive the subsequent data until
being disabled by the controller after the controller has received a complete message from
the ‘master’ station. If the controller does not disable the receiver after receiving a
message from the ‘master’ station, the receiver will generate a parity error upon receiving
another address byte. The controller then determines if the address byte addresses its ID
address, if it is not, the controller then can disable the receiver. If the address byte
addresses the ‘slave’ ID address, the controller take no further action; the receiver will
receive the subsequent data.
If Special Character Detect is enabled (EFR[5] is set and XOFF2 contains the address
byte) the receiver will try to detect an address byte that matches the programmed
character in XOFF2. If the received byte is a data byte or an address byte that does not
match the programmed character in XOFF2, the receiver will discard these data. Upon
receiving an address byte that matches the XOFF2 character, the receiver will be
automatically enabled if not already enabled, and the address character is pushed into the
RX FIFO along with the parity bit (in place of the parity error bit). The receiver also
generates a line status interrupt (IER bit 2 must be set to 1 at this time). The receiver will
then receive the subsequent data from the ‘master’ station until being disabled by the
controller after having received a message from the ‘master’ station.
If another address byte is received and this address byte does not match XOFF2
character, the receiver will be automatically disabled and the address byte is ignored. If
the address byte matches XOFF2 character, the receiver will put this byte in the RX FIFO
along with the parity bit in the parity error bit (LSR[2]).
Rev. 06 — 19 December 2006
Dual UART with I
2
SC16IS752/SC16IS762
C-bus/SPI interface, 64-byte FIFOs, IrDA SIR
© NXP B.V. 2006. All rights reserved.
34 of 59