xr16l2552im Exar Corporation, xr16l2552im Datasheet - Page 8

• Manufacturer Part Number: xr16l2552im
• Description: Industry Smallest Package Uart With 2.25v To 5.5v Operation
• Manufacturer: Exar Corporation

XR16L2552
2.25V TO 5.5V DUART WITH 16-BYTE FIFO
The UART provides the user with the capability to bi-directionally transfer information between an external
CPU and an external serial communication device. A logic 0 on chip select pin (CS#) allows the user to select
the UART and then using the channel select (CHSEL) pin, the user can select channel A or B to configure,
send transmit data and/or unload receive data to/from the UART. Individual channel select functions are shown
in
Each UART channel in the L2552 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 and dual ST16C2550. 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), and a user accessible scratchpad register (SPR).
Beyond the general 16C2550 features and capabilities, the L2552 offers enhanced feature registers (AFR,
EFR, Xon/Xoff 1, Xon/Xoff 2) that provide automatic RTS and CTS hardware flow control, automatic Xon/Xoff
software flow control, and simultaneous writes to both channels. All the register functions are discussed in full
detail later in
During a write mode cycle, the setting of Alternate Function Register (AFR) bit-0 to a logic 1 will override the
CHSEL selection and allows a simultaneous write to both UART channel sections. This functional capability
allow the registers in both UART channels to be modified concurrently, saving individual channel initialization
time. Caution should be exercised, however, when using this capability. Any in-process serial data transfer
may be disrupted by changing an active channel’s mode.
The device does not support direct memory access. The DMA Mode (a legacy term) in this document doesn’t
mean “direct memory access” but refers to data block transfer operation. The DMA mode affects the state of
the RXRDY# A/B (MF# A/B becomes RXRDY# A/B output when AFR[2:1] = ‘10’) and TXRDY# A/B 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 FIFO are enabled and the DMA mode is disabled (FCR bit-3 = 0), the L2552 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 loading or unloading the FIFO in a block
sequence determined by the programmed trigger level. The following table show their behavior. Also see
Figure 18
2.5
2.6
2.7
2.8
Table
Channel A and B Selection
Channel A and B Internal Registers
Simultaneous Write to Channel A and B
DMA Mode
1.
through
“Section 3.0, UART INTERNAL REGISTERS” on page
Figure
23.
CS#
1
0
0
T
ABLE
CHSEL
1: C
X
1
0
HANNEL
8
A
AND
Channel A selected
Channel B selected
UART de-selected
F
B S
UNCTION
ELECT
21.
xr
REV. 1.1.1