XR16V654_0709 Datasheet, PDF (13/58 Pages) Exar Corporation – 2.25V TO 3.6V QUAD UART WITH 64-BYTE FIFO

XR16V654/654D
REV. 1.0.2
2.25V TO 3.6V QUAD UART WITH 64-BYTE FIFO
2.2 Device Reset
The RESET input resets the internal registers and the serial interface outputs in both channels to their default
state (see Table 17). An active high pulse of longer than 40 ns duration will be required to activate the reset
function in the device. Following a power-on reset or an external reset, the V654 is software compatible with
previous generation of UARTs, 16C454 and 16C554.
2.3 Channel Selection
The UART provides the user with the capability to bi-directionally transfer information between an external
CPU and an external serial communication device. During Intel Bus Mode (16/68# pin is connected to VCC), a
logic 0 on chip select pins, CSA#, CSB#, CSC# or CSD# allows the user to select UART channel A, B, C or D
to configure, send transmit data and/or unload receive data to/from the UART. Selecting all four UARTs can be
useful during power up initialization to write to the same internal registers, but do not attempt to read from all
four uarts simultaneously. Individual channel select functions are shown in Table 1.
TABLE 1: CHANNEL A-D SELECT IN 16 MODE
CSA# CSB# CSC# CSD#
FUNCTION
1
1
1
1
UART de-selected
0
1
1
1
Channel A selected
1
0
1
1
Channel B selected
1
1
0
1
Channel C selected
1
1
1
0
Channel D selected
0
0
0
0
Channels A-D selected
During Motorola Bus Mode (16/68# pin is connected to GND), the package interface pins are configured for
connection with Motorola, and other popular microprocessor bus types. In this mode the V654 decodes two
additional addresses, A3 and A4, to select one of the four UART ports. The A3 and A4 address decode
function is used only when in the Motorola Bus Mode. See Table 2.
TABLE 2: CHANNEL A-D SELECT IN 68 MODE
CS# A4 A3
FUNCTION
1
X
X
UART de-selected
0
0
0
Channel A selected
0
0
1
Channel B selected
0
1
0
Channel C selected
0
1
1
Channel D selected
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