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參數(shù)資料
| 型號： | DS1280 |
| 廠商： | Maxim Integrated Products, Inc. |
| 英文描述： | 3-Wire to Bytewide Converter Chip(3線至字節(jié)寬度（8位）轉(zhuǎn)換芯片) |
| 中文描述： | 3線，以Bytewide轉(zhuǎn)換器芯片（3線至字節(jié)寬度（8位）轉(zhuǎn)換芯片） |
| 文件頁數(shù)： | 5/11頁 |
| 文件大?。?/td> | 132K |
| 代理商： | DS1280 |
DS1280
021998 5/11
PROTOCOL
Figure 2
MSB
LSB
COMMAND FIELD
ADDRESS BITS
A18
BYTE 3
MSB
A15
LSB
ADDRESS BITS
A12
MSB
LSB
BYTE 2
BYTE 4
MSB
S15
LSB
SELECT BITS
S12
BYTE 5
MSB
LSB
CYCLIC REDUNDANCY CHECK
BYTE 6
MSB
LSB
BYTE 1
MSB
LSB
BYTE 0
SELECT BITS
S4
ADDRESS BITS
A4
READ/WRITE FUNCTION FIELD
F
A7
A6
A5
A3
A2
A1
A0
A14
A13
A11
A10
A9
A8
F
F
F
F
F
F
F
C
A17
A16
S7
S6
S5
S3
S2
S1
S0
S14
S13
S11
S10
S9
S8
X
X
X
X
X
X
X
X
C
C
C
C
In any 2-port system there is a potential for access colli-
sions. To solve this problem, an arbitration byte is pro-
vided so that the serial and parallel ports of the DS1280
can determine the status of the other port. A special
byte in RAM address space is reserved to allow for
handshaking between the two ports. This arbitration
byte has a special attribute in that it is simultaneously
accessible by both ports.
Two commands are used by the 3-wire serial port proto-
col to manage the arbitration byte. First, since this byte
will create a hole in RAM address space for the parallel
bytewide port, a command is added to move the arbitra-
tion byte to either address location ‘‘00000” or address
location ‘‘7FFFF.” When setting the arbitration byte ad-
dress location, the correct read/write field and com-
mand field must be entered along with all zeroes or all
ones in the address field. It is important to note that the
arbitration byte is located in the parallel memory loca-
tion assigned by the serial port using the appropriate
commands. However, the physical byte of RAM is lo-
cated within the DS1280. The existence of this physical
byte is transparent to the bytewide parallel port and
looks like normal RAM space with some read/write re-
striction. However, the serial port can still address the
actual RAM location at either 00000 or 7FFFF in addi-
tion to accessing the arbitration byte.
The second command used by the 3-wire serial port
provides for polling of the arbitration byte to determine
the status of the parallel port. In addition, the arbitration
byte can be set to indicate to the parallel port that the se-
rial port is taking over the RAM. The second command
protocol allows the serial port to do a compressed read-
write-read operation that causes the arbitration byte to
be read by the first eight clocks following the protocol.
The next eight clocks cause data to be written into the
arbitration byte, and the last eight clock cycles allow for
a second read of the data for verification. The 24 cycles
occur by entering the 56-bit protocol only once. The pro-
tocol pattern entered is a write function in the read/write
field (00010111) and the correct command field.
SELECT BITS
Three other commands are used to set the select bits in
the protocol. Once the select bits are set to a binary val-
ue they must be matched exactly when protocol is sent
or further activity is prevented. The bits allow for 65,536
different binary combinations. Therefore, multiple
DS1280s can be connected on the same serial bus and
only the appropriate device will respond. To write the
select bits, a write function in the read/write field is re-
quired along with the appropriate command in the com-
mand field.
To read the select bits, a read cycle in the read/write field
is required along with the appropriate command in the
command field. The arrangement of reading and writing
select bits allows the user to have multiple DS1280s in
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