XR16V654_0709 Datasheet, PDF (14/58 Pages) Exar Corporation – 2.25V TO 3.6V QUAD UART WITH 64-BYTE FIFO

XR16V654/654D
2.25V TO 3.6V QUAD UART WITH 64-BYTE FIFO
REV. 1.0.2
2.4 Channels A-D Internal Registers
Each UART channel in the V654 has a set of enhanced registers for controlling, monitoring and data loading
and unloading. The configuration register set is compatible to those already available in the standard single
16C550. These registers function as data holding registers (THR/RHR), interrupt status and control registers
(ISR/IER), a FIFO control register (FCR), receive line status and control registers (LSR/LCR), modem status
and control registers (MSR/MCR), programmable data rate (clock) divisor registers (DLL/DLM/DLD), and a
user accessible scratchpad register (SPR).
Beyond the general 16C550 features and capabilities, the V654 offers enhanced feature registers (EFR, Xon/
Xoff 1, Xon/Xoff 2, FSTAT) that provide automatic RTS and CTS hardware flow control and automatic Xon/Xoff
software flow control. All the register functions are discussed in full detail later in “Section 3.0, UART
INTERNAL REGISTERS” on page 26.
2.5 INT Ouputs for Channels A-D
The interrupt outputs change according to the operating mode and enhanced features setup. Table 3 and 4
summarize the operating behavior for the transmitter and receiver. Also see Figure 21 through 26.
TABLE 3: INT PIN OPERATION FOR TRANSMITTER FOR CHANNELS A-D
FCR BIT-0 = 0
(FIFO DISABLED)
FCR BIT-0 = 1 (FIFO ENABLED)
FCR Bit-3 = 0
(DMA Mode Disabled)
FCR Bit-3 = 1
(DMA Mode Enabled)
INT Pin LOW = a byte in THR
HIGH = THR empty
LOW = FIFO above trigger level
HIGH = FIFO below trigger level or
FIFO empty
LOW = FIFO above trigger level
HIGH = FIFO below trigger level or
FIFO empty
TABLE 4: INT PIN OPERATION FOR RECEIVER FOR CHANNELS A-D
FCR BIT-0 = 0
(FIFO DISABLED)
FCR BIT-0 = 1 (FIFO ENABLED)
FCR Bit-3 = 0
(DMA Mode Disabled)
FCR Bit-3 = 1
(DMA Mode Enabled)
INT Pin LOW = no data
HIGH = 1 byte
LOW = FIFO below trigger level
HIGH = FIFO above trigger level
LOW = FIFO below trigger level
HIGH = FIFO above trigger level
2.6 DMA Mode
The device does not support direct memory access. The DMA Mode (a legacy term) in this document does not
mean “direct memory access” but refers to data block transfer operation. The DMA mode affects the state of
the RXRDY# A-D and TXRDY# A-D output pins. The transmit and receive FIFO trigger levels provide
additional flexibility to the user for block mode operation. The LSR bits 5-6 provide an indication when the
transmitter is empty or has an empty location(s) for more data. The user can optionally operate the transmit
and receive FIFO in the DMA mode (FCR bit-3 = 1). When the transmit and receive FIFOs are enabled and the
DMA mode is disabled (FCR bit-3 = 0), the V654 is placed in single-character mode for data transmit or receive
operation. When DMA mode is enabled (FCR bit-3 = 1), the user takes advantage of block mode operation by
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