Data Sheet - Freescale Semiconductor

3.6.2 Response transmitter
The response transmitter block converts two digital signals into two supply modulation currents. The response currents are
generated such that the rise and fall times are the same whether the I RESP current is being transmitted or the 2 x I RESP current
is being transmitted. A diagram of the response transmitter is shown in Figure 29. Current values and timing parameters are
specified in Section 2.3 and Section 2.7.
3.6.3 Discovery Mode current sense
Figure 31. DSI3 transmitter block diagram
The current sense circuit is used during Discovery Mode to determine if any additional slaves are connected to the BUS_O pin
of the device. A diagram of the current sense circuit is shown in Figure 32. Current values and timing parameters are specified
in Section 2.3 and Section 2.7. Details regarding Discovery Mode are included in Section 4.1.3.
BUS_I
BUS_O
V HIGH
V LOW
I CCQ_SAMPLE
I RESP Activation
Disc_Compare
R SENSE Amp
t Disc_Dly
Transmit Level ‘0’
Transmit Level ‘1’
Transmit Level ‘2’
Magnitude
Control
Slew Control
Figure 32. Discovery Mode current sense circuit block diagram
t IDiscsamp_Dly
I OUT
I CCQ
Sample & Hold
t Disc_Iccqsamp
I CCQ Sample
t IDiscsamp
-
+
-
Figure 33. DSI3 Discovery Mode sensing timing diagram
MMA27XXW
Sensors
Freescale Semiconductor, Inc. 57
I REF
I CCQ
I DISC >0?
Disc_Compare
I DATA
V SS
Disc_Command_Rcvd
Control
Logic
AddrCount
LastDevice
t