User's Manual

User Manual
SM3000 OEM module
Functional description
The module uses SPI for its interface. The module is configured as SPI master, the host as SPI slave. The
clock speed is 1MHz More on timing later.
The module always starts SPI communication by signalling the DR (Data Ready) line. When data is available
for the host the module will transmit the data upon reception to the host using a “write” command. When
the host needs to send data to the module it must signal the RTS (Request To Send) line. The module will
then in due time send a “read” command to receive the data from the host. If both module and host have
data to send the module will issue a “read/write” command for full duplex communication. The drawings in
the following sections omit the CS line. The CS line will be pulled low to mark the start of a byte or a group
of bytes and is intended to function as a SPI hardware enable line for the Host.
Write command
If the module has data to send and the host does not, it will send a write command. The RTS line is kept high
by the host indicating that it has no data to send
1
. The module will lower the DR line to indicate the start of
communication.
The module will generate a clock signal on the SCLK line. The clock signal consists of groups of 8 pulses.
Each group represents one byte transmitted and received.
The first byte that is outputted on the MOSI line by the module is the write command: 0x35. The second byte
is N: the number of bytes the module will send afterwards. The host may put any data on the MISO line.
These values are ignored by the module. When all bytes are sent the module raises the DR line again to mark
end of communication.
1 The SM3000 features a 10K pull-up resistor on the RTS- and DR line
10/27 Ambient Systems B.V.