SC16C2552B_3
NXP B.V. 2009. All rights reserved.
Product data sheet
Rev. 03 — 12 February 2009
9 of 38
NXP Semiconductors
SC16C2552B
5 V, 3.3 V and 2.5 V dual UART, 5 Mbit/s (max.), with 16-byte FIFOs
6.6 DMA operation
The SC16C2552B FIFO trigger level provides additional exibility to the user for block
mode operation. LSR[6:5] provide an indication when the transmitter is empty or has an
empty location(s). The user can optionally operate the transmit and receive FIFOs in the
DMA mode (FCR[3]). When the transmit and receive FIFOs are enabled and the DMA
mode is de-activated (DMA Mode 0), the SC16C2552B activates the interrupt output pin
for each data transmit or receive operation. When DMA mode is activated (DMA Mode 1),
the user takes the advantage of block mode operation by loading or unloading the FIFO in
a block sequence determined by the receive trigger level and the transmit FIFO. In this
mode, the SC16C2552B sets the interrupt output pin when characters in the transmit
FIFO is below 16, or the characters in the receive FIFOs are above the receive trigger
level.
6.7 Loopback mode
The internal loopback capability allows on-board diagnostics. In the Loopback mode, the
normal modem interface pins are disconnected and recongured for loopback internally.
MCR[3:0] register bits are used for controlling loopback diagnostic testing. In the
Loopback mode, INT enable and MCR[2] in the MCR register (bits 3:2) control the modem
RI and CD inputs, respectively. MCR signals DTR (bit 0) and RTS (bit 1) are used to
control the modem DSR and CTS inputs, respectively. The transmitter output (TX) and the
receiver input (RX) are disconnected from their associated interface pins, and instead are
connected together internally (see
Figure 4). The CTS, DSR, CD, and RI are
disconnected from their normal modem control inputs pins, and instead are connected
internally to RTS, DTR, OP2 and OP1. Loopback test data is entered into the transmit
holding register via the user data bus interface, D0 to D7. The transmit UART serializes
the data and passes the serial data to the receive UART via the internal loopback
connection. The receive UART converts the serial data back into parallel data that is then
Table 5.
Baud rate generator programming table using a 1.8432 MHz clock
Output
baud rate
Output
16
× clock divisor
(decimal)
Output
16
× clock divisor
(HEX)
DLM
program value
(HEX)
DLL
program value
(HEX)
50
2304
900
09
00
75
1536
600
06
00
150
768
300
03
00
300
384
180
01
80
600
192
C0
00
C0
1200
96
60
00
60
2400
48
30
00
30
4800
24
18
00
18
7200
16
10
00
10
9600
12
0C
00
0C
19.2 k
6
06
00
06
38.4 k
3
03
00
03
57.6 k
2
02
00
02
115.2 k
1
01
00
01