XR16V2750 Datasheet, PDF (7/51 Pages) Exar Corporation – HIGH PERFORMANCE DUART WITH 64-BYTE FIFO

REV. P1.0.0
2.0 FUNCTIONAL DESCRIPTIONS
2.1 CPU Interface
PRELIMINARY
XR16V2750
HIGH PERFORMANCE DUART WITH 64-BYTE FIFO
The CPU interface is 8 data bits wide with 3 address lines and control signals to execute data bus read and
write transactions. The V2750 data interface supports the Intel compatible types of CPUs and it is compatible
to the industry standard 16C550 UART. No clock (oscillator nor external clock) is required to operate a data
bus transaction. Each bus cycle is asynchronous using CS#, IOR# and IOW# signals. Both UART channels
share the same data bus for host operations. The data bus interconnections are shown in Figure 3.
FIGURE 3. XR16V2750 DATA BUS INTERCONNECTIONS
D0
D1
D2
D3
D4
D5
D6
D7
A0
A1
A2
IOR#
IOW #
UART_CSA#
UART_CSB#
UART_INTA
UART_INTB
TXRDYA#
RXRDYA#
TXRDYB#
RXRDYB#
UART_RESET
D0
D1
D2
D3
D4
D5
D6
D7
A0
A1
A2
IOR#
IOW #
UART
Channel A
CSA#
CSB#
INTA
INTB
UART
Channel B
TXRDYA#
RXRDYA#
TXRDYB#
RXRDYB#
VCC
TXA
RXA
DTRA#
R TS A#
C TS A#
DSRA#
CDA#
RIA#
OP2A#
TXB
RXB
DTRB#
R TS B#
C TS B#
DSRB#
CDB#
RIB#
OP2B#
RESET
GND
VCC
Serial Interface of
RS-232, RS-485
Serial Interface of
RS-232, RS-485
2750int
2.2 5-Volt Tolerant Inputs
The V2750 can accept up to 5V inputs even when operating at 3.3V or 2.5V. But note that if the V2750 is
operating at 2.5V, its V_OH may not be high enough to meet the requirements of the V_IH of a CPU or a serial
transceiver that is operating at 5V. Caution: XTAL1 is not 5 volt tolerant.
2.3 Device Reset
The RESET input resets the internal registers and the serial interface outputs in both channels to their default
state (see Table 16). An active high pulse of longer than 40 ns duration will be required to activate the reset
function in the device.
2.4 Device Identification and Revision
The XR16V2750 provides a Device Identification code and a Device Revision code to distinguish the part from
other devices and revisions. To read the identification code from the part, it is required to set the baud rate
generator registers DLL and DLM both to 0x00 (DLD = 0xXX). Now reading the content of the DLM will provide
0x0A for the XR16V2750 and reading the content of DLL will provide the revision of the part; for example, a
reading of 0x01 means revision A.
2.5 Channel A and B Selection
The UART provides the user with the capability to bi-directionally transfer information between an external
CPU and an external serial communication device. A LOW signal on the chip select pins, CSA# or CSB#,
allows the user to select UART channel A or B to configure, send transmit data and/or unload receive data to/
from the UART. Selecting both UARTs can be useful during power up initialization to write to the same internal
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