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DS3900 Datasheet(PDF) 6 Page - Maxim Integrated Products

Part No. DS3900
Description  Serial Communications Module For Evaluation Kits
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Maker  MAXIM [Maxim Integrated Products]
Homepage  http://www.maxim-ic.com

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Serial Communications Module
For Evaluation Kits
Using the DS3900 with 2-Wire Devices
There are two modes that can be used to communicate
with 2-wire devices. There is an individual command
mode that allows the PC to control exactly what is writ-
ten over the 2-wire bus, and a packet-based mode that
automatically sends the start, device address, data
address, and the stop commands.
When using the individual command mode, the PC
sends out individual commands to issue 2-wire start
conditions, stop conditions, write data, and read data
with or without acknowledgement. After each command
is sent, the DS3900 executes the command and returns
the individual 2-wire command's acknowledgement
code. If an error occurs, the DS3900 will return 0xFA.
For a complete listing of commands see Table 1.
To help with using the individual commands, two exam-
ples showing writing to and reading from a DS1803 are
shown in Tables 4 and 5. The assumption made for
addressing the DS1803 is that all three addressing pins
(A0, A1, and A2) are grounded. Packet mode was
added in revision 2.0 of the firmware, and it is support-
ed by 3 new commands: Set Packet Device Address
(0xA5); Packet Write (0x8%); and Packet Read (0x9%).
The Set Packet Device Address command is used to
set the 2-wire device address used by the Packet Read
and Packet Write commands. The Set Packet Device
Address command should be called before any packet
reads or writes to ensure that communications are initi-
ated at the intended device address. Once the packet
device address is set, it will remain set until it is
changed again by calling the Set Packet Device
Address function, or the power is cycled. Upon initial
power-up, this value is indeterminate, so it should be
reset to the desired value when there is any doubt
about its current state. If the value is successfully
changed, the DS3900 will return an acknowledgement
of 0xB5, and if an error occurs, 0xFA will be returned.
Note: The value sent to the DS3900 with the Set Packet
Device Address command should always be an even
value (e.g. 0xA0, 0xA2). The DS3900 automatically
controls the read/write bit of the device address during
packet read and write operations. Failure to send even
values will result in communication problems.
The Packet Write command allows up to 16 data bytes
to be sent from the PC to a 2-wire device with a single
command. The data will be written to the device
address set using the Set Packet Device Address com-
mand. To initiate a Packet Write command, the first
byte sent to the DS3900 is 0x8%, where % is one less
than the number of bytes to be written (e.g. 0x80 hex
writes one byte). The second byte sent to the DS3900
is the starting memory address to write the data, which
is followed immediately by %+1 data bytes. Once the
DS3900 has received the entire packet of data, it will
begin sending it to the 2-wire device. The Packet Write
command monitors the 2-wire communication to ensure
that the 2-wire device is acknowledging every byte of
the data transmission. If every byte of the Packet Write
is acknowledged, the DS3900 sends 0x8% back to the
PC. If all bytes are not acknowledged, the DS3900
returns 0xFA.
Because the Packet Write forces the following order of
events during the 2-wire communication to be: start
condition, write the device address, write the memory
address, write the data[1...16], stop condition, it may
not work with all devices. Use the individual 2-wire
commands if the packet write is not compatible with a
particular 2-wire device.
DS3900 PIN
Table 2. Bit I/O Addresses
DSIO r1.0
Original Issue. P3 is not
utilized for the pulse
function, it is open-
collector I/O only.
DSIO r1.1
The pulse functions were
added, changing P3’s
primary function.
Commands 0xC0 and
0xC1 were added.
DSIO r2.0
Major rev = 2
Minor rev = 0
Packet read and write,
packet address, and
read revision commands
Table 3. DS3900 Revisions

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