DS2407 Ver la hoja de datos (PDF) - Dallas Semiconductor -> Maxim Integrated
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DS2407 Datasheet PDF : 31 Pages
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DS2407
The output transistors of both channels are controlled
by their channel flip–flops. These flip–flops are accessi-
ble through bit locations 5 and 6 of Status Memory
address 7 as well as through the Channel Access com-
mand. Setting a channel flip–flop to 0 will make the
associated PIO–transistor conducting or on, setting the
flip–flop to 1 will switch the transistor off. When powering
up, the output transistors of both channels are non–con-
ducting or off. They may change their status as the
user–programmed power–on status is transferred into
Status Memory location 7. Bit 7 of Status Memory Loca-
tion 7 indicates if the DS2407 is connected to an exter-
nal power supply. Without external supply this read–
only bit will be 0. If the voltage applied to the VCC pin is
high enough to keep the device powered up, this bit will
be 1.
The Status Memory is programmed similarly to the data
memory. Details for reading and programming the sta-
tus memory portion of the DS2407 are given in the
Memory Function Commands section.
MEMORY FUNCTION COMMANDS
The “Memory Function Flow Chart” (Figure 6) describes
the protocols necessary for accessing the various data
fields and PIO channels within the DS2407. The
Memory Function Control section, 8–bit scratchpad,
and the Program Voltage Detect circuit combine to inter-
pret the commands issued by the bus master and create
the correct control signals within the device. A three–
byte protocol is issued by the bus master. It is comprised
of a command byte to determine the type of operation
and two address bytes to determine the specific starting
byte location within a data field or to supply and
exchange setup and status data when accessing the
PIO channels. The command byte indicates if the
device is to be read or written or if the PIO channels are
to be accessed. Writing data involves not only issuing
the correct command sequence but also providing a
12–volt programming voltage at the appropriate times.
To execute a write sequence, a byte of data is first
loaded into the scratchpad and then programmed into
the selected address. Write sequences always occur a
byte at a time. To execute a read sequence, the starting
address is issued by the bus master and data is read
from the part beginning at that initial location and contin-
uing to the end of the selected data field or until a reset
sequence is issued. All bits transferred to the DS2407
and received back by the bus master are sent least sig-
nificant bit first.
READ MEMORY [F0h]
The Read Memory command is used to read data from
the 1024–bit EPROM data memory field. The bus mas-
ter follows the command byte with a two–byte address
(TA1=(T7:T0), TA2=(T15:T8)) that indicates a starting
byte location within the data field. Since the data
memory contains 128 bytes, T15:T8 and T7 should all
be zero. With every subsequent read data time slot the
bus master receives data from the DS2407 starting at
the initial address and continuing until the end of the
1024–bits data field is reached or until a Reset Pulse is
issued. If reading occurs through the end of memory
space, the bus master may issue sixteen additional read
time slots and the DS2407 will respond with a 16–bit
CRC of the command, address bytes and all data bytes
read from the initial starting byte through the last byte of
memory. This CRC is the result of clearing the CRC gen-
erator and then shifting in the command byte followed
by the two address bytes and the data bytes beginning
at the first addressed memory location and continuing
through to the last byte of the EPROM data memory.
After the CRC is received by the bus master, any subse-
quent read time slots will appear as logical 1s until a
Reset Pulse is issued. Any reads ended by a Reset
Pulse prior to reaching the end of memory will not have
the 16–bit CRC available.
Typically the software controlling the device should
store a 16–bit CRC with each page of data to insure
rapid, error–free data transfers that eliminate having to
read a page multiple times to determine if the received
data is correct or not. (See Book of DS19xx iButton
Standards, Chapter 7 for the recommended file struc-
ture to be used with the 1–Wire environment). If CRC
values are imbedded within the data it is unnecessary to
read the end–of–memory CRC. The Read Memory
command can be ended at any point by issuing a Reset
Pulse.
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