参数资料
| 型号： | SCC2681AC1N40,112 |
| 厂商： | NXP Semiconductors |
| 文件页数： | 7/29页 |
| 文件大小： | 0K |
| 描述： | IC UART DUAL 40-DIP |
| 产品培训模块： | Stand-Alone UARTs |
| 标准包装： | 9 |
| 特点： | 故障启动位检测 |
| 通道数： | 2，DUART |
| FIFO's： | 3 位 |
| 电源电压： | 5V |
| 带并行端口： | 是 |
| 带自动流量控制功能： | 是 |
| 带故障启动位检测功能： | 是 |
| 带CMOS： | 是 |
| 安装类型： | 通孔 |
| 封装/外壳： | 40-DIP（0.600"，15.24mm） |
| 供应商设备封装： | 40-DIP |
| 包装： | 管件 |
| 其它名称： | 568-3525-5 935274523112 SCC2681AC1N40 |
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Philips Semiconductors
Product data
SCC2681
Dual asynchronous receiver/transmitter (DUART)
2004 Apr 06
15
or transmitted character. Likewise, if a mode is deselected the
device will switch out of the mode immediately. An exception to this
is switching out of autoecho or remote loopback modes: if the
deselection occurs just after the receiver has sampled the stop bit
(indicated in autoecho by assertion of RxRDY), and the transmitter
is enabled, the transmitter will remain in autoecho mode until the
entire stop has been retransmitted.
MR2A[5] – Channel A Transmitter Request-to-Send Control
CAUTION: When the transmitter controls the OP pin (usually used
for the RTSN signal) the meaning of the pin is not RTSN at all!
Rather, it signals that the transmitter has finished the transmission
(i.e., end of block).
Note: Please see
Application Note AN10251 for more information
on this subject.
This bit allows deactivation of the RTSN output by the transmitter.
This output is manually asserted and negated by the appropriate
commands issued via the SOPR and ROPR registers. MR2[5] set to
1 caused the RTSN to be reset automatically one bit time after the
character(s) in the transmit shift register and in the THR (if any) are
completely transmitted (including the programmed number of stop
bits) if a previously issued transmitter disable is pending. This
feature can be used to automatically terminate the transmission as
follows:
1. Program the auto-reset mode: MR2[5]=1
2. Enable transmitter, if not already enabled
3. Set OPR[0] or OPR[1] to ‘1’ via the SOPR and ROPR registers
4. Send message
5. After the last character of the message is loaded to the THR,
disable the transmitter. (If the transmitter is underrun, a special
case exists. See note below.)
6. The last character will be transmitted and the RTSN will be reset
one bit time after the last stop bit is sent.
NOTE: The transmitter is in an underrun condition when both the
TxRDY and the TxEMT bits are set. This condition also exists
immediately after the transmitter is enabled from the disabled or
reset state. When using the above procedure with the transmitter in
the underrun condition, the issuing of the transmitter disable must be
delayed from the loading of a single, or last, character until the
TxRDY becomes active again after the character is loaded.
MR2A[4] – Channel A Clear-to-Send Control
If this bit is 0, CTSAN has no effect on the transmitter. If this bit is a
1, the transmitter checks the state of CTSAN (IPO) each time it is
ready to send a character. If IPO is asserted (LOW), the character is
transmitted. If it is negated (HIGH), the TxDA output remains in the
marking state and the transmission is delayed until CTSAN goes
LOW. Changes in CTSAN while a character is being transmitted do
not affect the transmission of that character..
MR2A[3:0] – Channel A Stop Bit Length Select
This field programs the length of the stop bit appended to the
transmitted character. Stop bit lengths of .563 TO 1 AND .563 to 2
bits. In increments of 0.625 bit, can be programmed for character
lengths of 6, 7, and 8 bits. For a character lengths of 5 bits, 1.0625
to 2 stop bits can be programmed in increments of .0625 bit.
The receiver only checks for a ‘mark’ condition at the center of the
first stop bit position (one bit time after the last data bit, or after the
parity bit is enabled) in all cases.
If an external 1
× clock is used for the transmitter, MR2A[3] = 0
selects one stop bit and MR2A[3] = 1 selects two stop bits to be
transmitted.
MR1B – Channel B Mode Register 1
MR1B is accessed when the Channel B MR pointer points to MR1.
The pointer is set to MR1 by RESET or by a ‘set pointer’ command
applied via CRB. After reading or writing MR1B, the pointer will point
to MR2B.
MR2B – Channel B Mode Register 2
MR2B is accessed when the Channel B MR pointer points to MR2,
which occurs after any access to MR1B. Accesses to MR2B do not
change the pointer.
The bit definitions for mode registers 1 and 2 are identical to the bit
definitions for MRA and MR2A except that all control actions apply
to the Channel B receiver and transmitter and the corresponding
inputs and outputs.
CSRA – Channel A Clock Select Register
STandard baud rates are shown below. A read at address 0x2
changes the baud rate generator to give higher speed baud rates.
(See Table 5 on page 21.) A subsequent read at address 0x2
changes the baud rate generator back to standard rates. In other
words, each read at 0x2 toggles the controlling flip-flop.
Table 3.
Bit Rate Generator Characteristics
Crystal or Clock = 3.6864MHz
Normal rate (baud)
Actual 16
× clock
(kHz)
Error (%)
50
0.8
0
75
1.2
0
110
1.759
–0.069
134.5
2.153
0.059
150
2.4
0
200
3.2
0
300
4.8
0
600
9.6
0
1050
16.756
–0.260
1200
19.2
0
1800
28.8
0
2000
32.056
0.175
2400
38.4
0
4800
76.8
0
7200
115.2
0
9600
153.6
0
14.4 k
230.4
0
19.2 k
307.2
0
28.8 k
460.8
0
38.4 k
614.4
0
57.6 k
921.6
0
115.2 k
1843.2 k
0
NOTE: Duty cycle of 16
× clock is 50% ± 1%.
Asynchronous UART communications can tolerate frequency error
of 4.1% to 6.7% in a “clean” communications channel. The percent
of error changes as the character length changes. The above
percentages range from 5 bits not parity to 8 bits with parity and one
stop bit. The error with 8 bits not parity and one stop bit is 4.6%. If a
stop bit length of 9/16 is used, the error tolerance will approach 0
due to a variable error of up to 1/16 bit time in receiver clock phase
alignment to the start bit.
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