XR16L2551_07 Datasheet, PDF (8/49 Pages) Exar Corporation – LOW VOLTAGE DUART WITH POWERSAVE

XR16L2551
LOW VOLTAGE DUART WITH POWERSAVE
REV. 1.1.3
2.0 FUNCTIONAL DESCRIPTIONS
2.1 CPU Interface
The CPU interface is 8 data bits wide with 3 address lines and control signals to execute data bus read and
write transactions. The L2551 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 CSA/B#, IOR# and IOW# or CS#, R/W# and A3 inputs.
Both UART channels share the same data bus for host operations. A typical data bus interconnection for Intel
and Motorola mode is shown in Figure 3.
FIGURE 3. XR16L2751 TYPICAL INTEL/MOTOROLA 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
A3
R/W#
UART_CS#
UART_IRQ#
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#
RTSA#
CTSA#
DSRA#
CDA#
RIA#
OP2A#
TXB
RXB
DTRB#
RTSB#
CTSB#
DSRB#
CDB#
RIB#
OP2B#
RESET
GND
Intel Data Bus Interconnections
2.25 to 5.5 Volt VCC
RS-232 Serial Interface
(no connect)
RS-232 Serial Interface
(no connect)
VCC
VCC
(no connect)
D0
D1
D2
D3
D4
D5
D6
D7
A0
A1
A2
CSB#
IOR#
IOW#
CSA#
UART
Channel A
INTA
INTB
UART
Channel B
TXRDYA#
RXRDYA#
TXRDYB#
RXRDYB#
RESET#
VCC
TXA
RXA
DTRA#
RTSA#
CTSA#
DSRA#
CDA#
RIA#
OP2A#
TXB
RXB
DTRB#
RTSB#
CTSB#
DSRB#
CDB#
RIB#
OP2B#
GND
Motorola Data Bus Interconnections
2.25 to 5.5 Volt VCC
RS-232 Serial Interface
(no connect)
RS-232 Serial Interface
(no connect)
2.2 5-Volt Tolerant Inputs
The L2551 can accept up to 5V inputs even when operating at 3.3V or 2.5V. But note that if the L2551 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.
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