ST16C2552CJ44 EXAR [Exar Corporation], ST16C2552CJ44 Datasheet - Page 8

• Manufacturer Part Number: ST16C2552CJ44
• Description: 2.97V TO 5.5V DUAL UART WITH 16-BYTE FIFO
• Manufacturer: EXAR [Exar Corporation]

ST16C2552
2.97V TO 5.5V DUAL UART WITH 16-BYTE FIFO
Each UART channel in the 2552 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 2552 offers the Alternate Function Register which
allows simultaneous writes to both channels. All the register functions are discussed in full detail later in
“Section 3.0, UART INTERNAL REGISTERS” on page
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 2552 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
Figures
2.4
2.5
2.6
RXRDY# A/B
TXRDY# A/B
P
INS
Channel A and B Internal Registers
Simultaneous Write to Channel A and B
DMA Mode
16
through 21.
0 = 1 byte.
1 = no data.
0 = THR empty.
1 = byte in THR.
(FIFO D
FCR
T
ABLE
BIT
ISABLED
-0=0
2: TXRDY#
)
0 = at least 1 byte in FIFO
1 = FIFO empty.
0 = FIFO empty.
1 = at least 1 byte in FIFO.
(DMA Mode Disabled)
AND
FCR Bit-3 = 0
RXRDY# O
8
UTPUTS IN
15.
FCR B
IT
-0=1 (FIFO E
FIFO
1 to 0 transition when FIFO reaches the trigger
level, or timeout occurs.
0 to 1 transition when FIFO empties.
0 = FIFO has at least 1 empty location.
1 = FIFO is full.
AND
DMA M
(DMA Mode Enabled)
NABLED
FCR Bit-3 = 1
ODE
)
REV. 4.2.1