參數(shù)資料
型號(hào)： SCC2681AC1A44,518
廠商： NXP Semiconductors
文件頁(yè)數(shù)： 13/29頁(yè)
文件大?。?/td> 0K
描述： IC DUART 44-PLCC
標(biāo)準(zhǔn)包裝： 500
特點(diǎn)： 故障啟動(dòng)位檢測(cè)
通道數(shù)： 2，DUART
FIFO's： 3 位
電源電壓： 5V
帶并行端口： 是
帶自動(dòng)流量控制功能： 是
帶故障啟動(dòng)位檢測(cè)功能： 是
帶CMOS： 是
安裝類型： 表面貼裝
封裝/外殼： 44-LCC（J 形引線）
供應(yīng)商設(shè)備封裝： 44-PLCC
包裝： 帶卷 (TR)
其它名稱： 935274521518
SCC2681AC1A44-T
SCC2681AC1A44-T-ND
Philips Semiconductors
Product data
SCC2681
Dual asynchronous receiver/transmitter (DUART)
2004 Apr 06
20
masked off through the OPCR[3:2] = 00 until the T/C is programmed
to the desired operational state.
In the counter mode, the C/T counts down the number of pulses
loaded into CTUR and CTLR by the CPU. Counting begins upon
receipt of a counter command. Upon reaching terminal count
(0x0000), the counter ready interrupt bit (ISR[3]) is set. The counter
continues counting past the terminal count until stopped by the CPU.
If OP3 is programmed to be the output of the C/T, the output
remains HIGH until terminal count is reached, at which time it goes
LOW. The output returns to the HIGH state and ISR[3] is cleared
when the counter is stopped by a stop counter command. The CPU
may change the values of CTUR and CTLR at any time, but the new
count becomes effective only on the next start counter command. If
new values have not been loaded, the previous count values are
preserved and used for the next count cycle.
In the counter mode, the current value of the upper and lower 8 bits
of the counter (CTU, CTL) may be read by the CPU.
It is recommended that the counter be stopped when reading to
prevent potential problems which may occur if a carry from the lower
8 bits to the upper 8 bits occurs between the times that both halves
of the counter are read. However, note that a subsequent start
counter command will cause the counter to begin a new count cycle
using the values in CTUR and CTLR.
Output Port Notes
The output ports are controlled from three places: the OPCR
register, the OPR register, and the MR registers. The default source
of data for the OP[7:0] pins is the OPR register. When the OPR is
the source for the OP pins, the pins will drive the complement
(inverse) of data in the OPR register.
The OPCR register, the MR register, and the Command register
control the data source for the OP pins. It is this ‘multi-source’
feature of the OP pins that allows them to give the 485 turn-around
RTS, DMA, interrupt and various other internal clock signals.
The OPCR controls the source of the data for the output ports OP2
through OP7. The data source for output ports OP0 and OP1 is
controlled by the MR and CR registers. When the OPR is the source
of the data for the output ports, the data at the ports is inverted from
that in the OPR register.
The content of the OPR register is controlled by the Set and Reset
Output Port Bits ‘Commands’. These commands are actually the
addresses at 0xE and 0xF, respectively. When these commands are
used, action takes place only at the bit locations where ones exist
on the data bus. For example, a one in bit location 5 of the data
word used with the ‘Set Output Port Bits’ command will result in
OPR[5] being set to one. The OP[5] pin would then drive a logical
zero (VSS). Similarly, a one in bit position 5 of the data word
associated with the ‘Reset Output Ports Bits’ command would set
OPR[5] to zero, and hence, the pin OP[5] will drive to a one (VDD).
The use of two register locations to control the OPR relieves the
software from the burden of keeping a copy of the OPR settings and
thus facilitates a bit type manipulation of the individual bits. This is
the same reasoning used in the lower four bits of the command
register where the Rx and Tx enabling is controlled.
The CTS, RTS, CTS Enable Tx signals
CTS (Clear To Send) is usually meant to be a signal to the
transmitter meaning that it may transmit data to the receiver. The
CTS input is on pin IP0 for TxA and on IP1 for TxB. The CTS signal
is active LOW; thus, it is called CTSAN for TxA and CTSBN for TxB.
RTS is usually meant to be a signal from the receiver indicating that
the receiver is ready to receive data. It is also active LOW and is,
thus, called RTSAN for RxA and RTSBN for RxB. RTSAN is on pin
op0 and RTSBN is on OP1. A receiver’s RTS output will usually be
connected to the CTS input of the associated transmitter. Therefore,
one could say that RTS and CTS are different ends of the same
wire!
MR2(4) is the bit that allows the transmitter to be controlled by the
CTS pin (IP0 or IP1). When this bit is set to one AND the CTS input
is driven HIGH, the transmitter will stop sending data at the end of
the present character being serialized. It is usually the RTS output of
the receiver that will be connected to the transmitter’s CTS input.
The receiver will set RTS HIGH when the receiver FIFO is full AND
the start bit of the fourth character is sensed. Transmission then
stops with four valid characters in the receiver. When MR2(4) is set
to one, CTSN must be at zero for the transmitter to operate. If
MR2(4) is set to zero, the IP pin will have no effect on the operation
of the transmitter.
MR1(7) is the bit that allows the receiver to control OP0. When OP0
(or OP1) is controlled by the receiver, the meaning of that pin will be
RTS. However, a point of confusion arises in that OP0 (or OP1) may
also be controlled by the transmitter. When the transmitter is
controlling this pin, its meaning is not RTS at all. It is, rather, that the
transmitter has finished sending its last data byte. Programming the
OP0 or OP1 pin to be controlled by the receiver and the transmitter
at the same time is allowed, but would usually be incompatible.
RTS is expressed at the OP0 or OP1 pin which is still an output port.
Therefore, the state of OP0 or OP1 should be set LOW for the
receiver to generate the proper RTS signal. The logic at the output is
basically a NAND of the OPR register and the RTS signal as
generated by the receiver. When the RTS flow control is selected via
the MR(7) bit state of the OPR register is not changed. Terminating
the use of “Flow Control” (via the MR registers) will return the OP0
or OP1 pins to the control of the OPR register.
Transmitter Disable Note
The sequence of instructions enable transmitter — load transmit
holding register — disable transmitter will result in nothing being
sent if the time between the end of loading the transmit holding
register and the disable command is less that 3/16 bit time in the
16x mode or one bit time in the 1x mode. Also, if the transmitter,
while in the enabled state and underrun condition, is immediately
disabled after a single character is loaded to the transmit holding
register, that character will not be sent.
In general, when it is desired to disable the transmitter before the
last character is sent AND the TxEMT bit is set in the status register
(TxEMT is always set if the transmitter has underrun or has just
been enabled), be sure the TxRDY bit is active immediately before
issuing the transmitter disable instruction. TxRDY sets at the end of
the “start bit” time. It is during the start bit that the data in the
transmit holding register is transferred to the transmit shift register.
Non-standard baud rates are available as shown in Table 5 below,
via the BRG Test function.
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