IN16C1054
6.3.3 Xon Any Function
While RX Software flow control function is enabled, data in TX FIFO are transmitted when
received Xon character and transmission is suspended when Xoff character is received.
This status is called ‘XOFF status’. Transmission is re-started when status changes to
‘XON status’ by incoming Xon character or Xon Any function that changes status when
any data arrives. Xon Any function is enabled if MCR[5] is set to ‘1’. While it is enabled,
XOFF status changes to XON status though Xoff character arrives.
Details about it are described in 6.3.2 Receive Software Flow Control.
6.3.4 Xoff Re-transmit Function
While TX Software flow control function is active, Xoff character is transmitted when the
amount of data in RX FIFO exceeds the value of FUR. Though it received Xoff character,
external UART may not recognize this character for some reason and continue to transmit
data. Under TX Software flow control, because Xoff character had been transmitted once
before, it is not transmitted again though more data arrive. In this situation, overflow may
occur in RX FIFO. Conventional UARTs can not deal this situation but SB16C1054 does
with Xoff Re-transmit function.
Xoff Re-transmit function transmits Xoff character again when more data arrives from
external UART though it transmitted Xoff character before. By this function the external
UART can recognize Xoff character and stop transmitting data though it didn’t recognize
the Xoff character before.
There are four Xoff Re-transmitting settings by XRCR[1:0]. Xoff character can be re-
transmitted when every 1, 4, 8 or 16 data arrives in XOFF status.
If XRCR[1:0] is ‘00’, Xoff character is re-transmitted whenever 1 more data arrives in
XOFF status. If XRCR[1:0] is ‘01’, Xoff character is re-transmitted whenever 4 more data
arrives in XOFF status. If ‘10’, 8 more data and if ‘11’, 16 more data. If the value of FUR is
approaching the FIFO size, 256-byte, it is good to write XRCR[1:0] ‘00’. If the 256-FUR
value is small, it is good to select ‘00’ of XRCR and if large, it is good to select ‘11’.
Xoff Re-transmit function is enabled by MCR[6] and MCR[2]. Change MCR[2] from OP1#
function to Xoff Re-transmit function by setting MCR[6] to ‘1’ and set MCR[2] to ‘1’ again.
Then Xoff Re-transmit function is enabled. When disabling it, first set MCR[6] to ‘1’ and
then clear MCR[2] to ‘0’.
Rev. 00
IKSEMICON [ IK SEMICON CO., LTD ]
