參數(shù)資料
型號: MAX1459
廠商: Maxim Integrated Products, Inc.
英文描述: 2-Wire, 4-20mA Smart Signal Conditioner
中文描述: 2線、4-20mA智能信號調(diào)理器
文件頁數(shù): 11/24頁
文件大小: 243K
代理商: MAX1459
Data Input/Output
The DIO line is an input/output pin used to issue com-
mands to the MAX1459 (input mode) or read the
EEPROM contents (output mode).
In input mode (the default mode), data on DIO is
latched on each rising edge of SCLK. Therefore, data
on DIO must be stable at the rising edge of SCLK and
should transition on the falling edge of SCLK.
DIO will switch to output mode after receiving either the
READ EEPROM command or the READ EEPROM
MATRIX command. See the
Read EEPROM
section for
detailed information.
Communication Protocol
To initiate communication, the first 8 bits on DIO after
CS transitions from low to high
must
be 101010U0 (AA
hex or A8 hex, defined as the INIT sequence). The
MAX1459 will then begin accepting 16-bit control
words (Figure 4).
If the INIT SEQUENCE is not detected, all subsequent
data on DIO is ignored until CS again transitions from
low to high and the correct INIT SEQUENCE is received.
The U bit of the INIT SEQUENCE controls the updating
of the DACs and configuration register from the internal
EEPROM. If this bit is low (U = 0, INIT SEQUENCE = A8
hex), all four internal DACs and the configuration regis-
ter will be updated from the EEPROM on the next rising
edge of CS (this is also the default on power-up). If the
U bit is high (INIT SEQUENCE = AA hex), the DACs
and configuration register will not be updated from the
internal EEPROM; they will retain their current value on
any subsequent CS rising edge. The MAX1459 contin-
ues to accept control words until CS is brought low.
Control Words
After receiving the INIT SEQUENCE on DIO, the
MAX1459 begins latching in 16-bit control words, MSB
first (Figure 5).
The first 4 bits of the control word (the MSBs,
CM3–CM0) are the command field. The last 12 bits
(D11–D0) represent the data field. The MAX1459 sup-
ports the commands listed in Table 5.
No-OP Command (0 hex)
The no-operation (No-OP) command must be issued
before and after the commands ERASE EEPROM and
WRITE EEPROM BIT. In the case of the ERASE EEP-
ROM command, the control word must be 0000 hex. In
the case of the WRITE EEPROM BIT command, the
command field must be 0h, and the data field must
have, in its lower bits, the EEPROM address to be writ-
ten (Figure 6). For example, to write location 1C hex of
M
2-Wire, 4–20mA
Smart Signal Conditioner
______________________________________________________________________________________
11
Figure 5. Control-Word Timing Diagram
SCLK
DIO
COMMAND
MSB
LSB
LSB
MSB
MSB
LSB
DATA
16-BIT CONTROL WORD
D9
D6
D8
D5
D7
D4
D3
D2
D1
D0
CM3
CM0
CM2
D11
CM1
D10
Figure 4. Communication Sequence
CS
SCLK
DIO
t
MIN
= 1.5ms
16 CLK
CYCLES
INIT
SEQUENCE
CONTROL
WORD
CONTROL
WORD
CONTROL
WORDS
16 CLK
CYCLES
n x 16 CLK
CYCLES
X
1
0
1
CM3
CM3
CM2
CM2
DO
DO
0
U
0
1
0
8 CLK
CYCLES
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