XRT16C854 Datasheet, PDF (35/54 Pages) Exar Corporation – 2.97V TO 5.5V QUAD UART WITH 128-BYTE FIFO

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REV. 3.0.1
XR16C854/854D
2.97V TO 5.5V QUAD UART WITH 128-BYTE FIFO
MSR[7]: CD Input Status
CD# (active high, logical 1). Normally this bit is the compliment of the CD# input. In the loopback mode this bit
is equivalent to bit-3 in the MCR register. The CD# input may be used as a general purpose input when the
modem interface is not used.
4.10 Scratch Pad Register (SPR) - Read/Write
This is a 8-bit general purpose register for the user to store temporary data. The content of this register is
preserved during sleep mode but becomes 0xFF (default) after a reset or a power off-on cycle.
4.11 Enhanced Mode Select Register (EMSR)
This register replaces SPR (during a Write) and is accessible only when FCTR[6] = 1.
EMSR[1:0]: Receive/Transmit FIFO Count (Write-Only)
When Scratchpad Swap (FCTR[6]) is asserted, EMSR bits 1-0 controls what mode the FIFO Level Counter is
operating in.
TABLE 14: SCRATCHPAD SWAP SELECTION
FCTR[6]
EMSR[1]
EMSR[0] Scratchpad is
0
X
X
Scratchpad
1
0
0
RX FIFO Counter Mode
1
0
1
TX FIFO Counter Mode
1
1
0
RX FIFO Counter Mode
1
1
1
Alternate RX/TX FIFO Counter Mode
During Alternate RX/TX FIFO Counter Mode, the first value read after EMSR bits 1-0 have been asserted will
always be the RX FIFO Counter. The second value read will correspond with the TX FIFO Counter. The next
value will be the RX FIFO Counter again, then the TX FIFO Counter and so on and so forth.
EMSR[3:2]: Reserved
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