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參數(shù)資料
| 型號： | 933662770129 |
| 廠商： | NXP SEMICONDUCTORS |
| 元件分類： | 微控制器/微處理器 |
| 英文描述： | 2 CHANNEL(S), 1M bps, SERIAL COMM CONTROLLER, PDIP28 |
| 封裝： | 0.600 INCH, PLASTIC, MO-015AH, SOT-117-1, DIP-28 |
| 文件頁數(shù)： | 2/34頁 |
| 文件大?。?/td> | 313K |
| 代理商： | 933662770129 |
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Philips Semiconductors
Product specification
SCN2681
Dual asynchronous receiver/transmitter (DUART)
1998 Sep 04
10
the FIFO pointers and result in the reading of previously read data.
A receiver reset will re-align the pointers.
Multidrop Mode
The DUART is equipped with a wake up mode for multidrop
applications. This mode is selected by programming bits MR1A[4:3]
or MR1B[4:3] to ‘11’ for Channels A and B, respectively. In this
mode of operation, a ‘master’ station transmits an address character
followed by data characters for the addressed ‘slave’ station. The
slave stations, with receivers that are normally disabled, examine
the received data stream and ‘wake up’ the CPU (by setting RxRDY)
only upon receipt of an address character. The CPU compares the
received address to its station address and enables the receiver if it
wishes to receive the subsequent data characters. Upon receipt of
another address character, the CPU may disable the receiver to
initiate the process again.
A transmitted character consists of a start bit, the programmed
number of data bits, and Address/Data (A/D) bit, and the
programmed number of stop bits. The polarity of the transmitted
A/D bit is selected by the CPU by programming bit
MR1A[2]/MR1B[2]. MR1A[2]/MR1B[2] = 0 transmits a zero in the
A/D bit position, which identifies the corresponding data bits as data
while MR1A[2]/MR1B[2] = 1 transmits a one in the A/D bit position,
which identifies the corresponding data bits as an address. The
CPU should program the mode register prior to loading the
corresponding data bits into the THR.
In this mode, the receiver continuously looks at the received data
stream, whether it is enabled or disabled. If disabled, it sets the
RxRDY status bit and loads the character into the RHR FIFO if the
received A/D bit is a one (address tag), but discards the received
character if the received A/D bit is a zero (data tag). If enabled, all
received characters are transferred to the CPU via the RHR. In
either case, the data bits are loaded into the data FIFO while the
A/D bit is loaded into the status FIFO position normally used for
parity error (SRA[5] or SRB[5]). Framing error, overrun error, and
break detect operate normally whether or not the receive is enabled.
PROGRAMMING
The operation of the DUART is programmed by writing control words
into the appropriate registers. Operational feedback is provided via
status registers which can be read by the CPU. The addressing of
the registers is described in Table 1.
The contents of certain control registers are initialized to zero on
RESET. Care should be exercised if the contents of a register are
changed during operation, since certain changes may cause
operational problems.
For example, changing the number of bits per character while the
transmitter is active may cause the transmission of an incorrect
character. In general, the contents of the MR, the CSR, and the
OPCR should only be changed while the receiver(s) and
transmitter(s) are not enabled, and certain changes to the ACR
should only be made while the C/T is stopped.
Mode registers 1 and 2 of each channel are accessed via
independent auxiliary pointers. The pointer is set to MR1x by
RESET or by issuing a ‘reset pointer’ command via the
corresponding command register. Any read or write of the mode
register while the pointer is at MR1x, switches the pointer to MR2x.
The pointer then remains at MR2x, so that subsequent accesses are
always to MR2x unless the pointer is reset to MR1x as described
above.
Mode, command, clock select, and status registers are duplicated
for each channel to provide total independent operation and control.
Refer to Table 2 for register bit descriptions.
The reserved
registers at addresses H‘02’ and H‘OA’ should never be read during
normal operation since they are reserved for internal diagnostics.
Table 1.
SCN2681 Register Addressing
A3
A2
A1
A0
READ (RDN = 0)
WRITE (WRN = 0)
0
Mode Register A (MR1A, MR2A)
0
1
Status Register A (SRA)
Clock Select Register A (CSRA)
0
1
0
BRG Test *
Command Register A (CRA)
0
1
Rx Holding Register A (RHRA)
Tx Holding Register A (THRA)
0
1
0
Input Port Change Register (IPCR)
Aux. Control Register (ACR)
0
1
0
1
Interrupt Status Register (ISR)
Interrupt Mask Register (IMR)
0
1
0
Counter/Timer Upper Value (CTU)
C/T Upper Preset Value (CRUR)
0
1
Counter/Timer Lower Value (CTL)
C/T Lower Preset Value (CTLR)
1
0
Mode Register B (MR1B, MR2B)
1
0
1
Status Register B (SRB)
Clock Select Register B (CSRB)
1
0
1
0
1X/16X Test
Command Register B (CRB)
1
0
1
Rx Holding Register B (RHRB)
Tx Holding Register B (THRB)
1
0
*Reserved*
1
0
1
Input Ports IP0 to IP6
Output Port Conf. Register (OPCR)
1
0
Start Counter Command
Set Output Port Bits Command
1
Stop Counter Command
Reset Output Port Bits Command
* See Table 5 for BRG Test frequencies in this data sheet, and
“Extended baud rates for SCN2681, SCN68681, SCC2691, SCC2692,
SCC68681 and SCC2698B” in application notes elsewhere in this publication.
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