Data Sheet - Freescale Semiconductor

3.3.2 BUS_I, V BUF , V REG , V REGA , undervoltage monitor
A circuit is incorporated to monitor the BUS_I supply voltage and the internally regulated voltages, V BUF, V REG and V REGA. If any
of the voltages fall below the specified undervoltage thresholds in Section 2.3, the device will be react as listed below.
• BUS_I
MMA27XXW
— If BUS_I falls below the specified threshold at any time, the BUSI_UV_ERR bit is set in the DEVSTAT2 register.
The BUS_I_UV_ERR bit will be cleared once the supply returns above the threshold and either one Periodic Data
Collection Mode status is transmitted with the VBUF_ERR bit set, or a response to a Command and Response
Mode Register Read of the DEVSTAT2 register is transmitted.
— If BUS_I falls below the specified threshold during a command transmission in Command and Response Mode, the
command is ignored, and no DSI3 response transmission occurs. Once the supply returns above the threshold, the
device will resume decoding commands.
— If BUS_I falls below the specified threshold during a response transmission in Command and Response Mode, the
response is terminated. No attempt is made to resend the response. Once the supply returns above the threshold,
the device will resume decoding commands.
— If BUS_I falls below the specified threshold during a command transmission in Periodic Data Collection Mode, the
command is ignored and no periodic response occurs during that period. Once the supply returns above the
threshold, the device will resume periodic transmissions in response to commands. The device will resume
decoding Background Diagnostic Mode commands after the Start Condition is met.
— If BUS_I falls below the specified threshold during a periodic response transmission in Periodic Data Collection
Mode, the response is terminated. No attempt is made to resend the response. Once the supply returns above the
threshold, the device will resume periodic transmissions in response to commands. The device will resume
decoding Background Diagnostic Mode commands after the Start Condition is met.
— If BUS_I falls below the specified threshold during a Background Diagnostic Mode response transmission in
Periodic Data Collection Mode, the response is terminated. No attempt is made to resend the response. Once the
supply returns above the threshold, the device will resume periodic transmissions in response to commands. The
device will resume decoding Background Diagnostic Mode commands after the Start Condition is met.
• VBUF — If VBUF falls below the specified threshold at any time, the VBUF_UV_ERR bit is set in the DEVSTAT2 register. If a
response transmission is in process, the response is terminated. No attempt is made to resend the response. Once
the supply returns above the threshold, the device will resume decoding commands and transmission of responses.
The VBUF_UV_ERR bit will be cleared once the supply returns above the threshold and one Periodic Data
Collection Mode status is transmitted with the VBUF_UV_ERR bit set.
• VREG or VREGA — If VREG or VREGA falls below the specified threshold at any time, the device is reset.
Reference Figure 7 for an example of a supply line interruption during a response in Periodic Data Collection Mode.
Sensors
34 Freescale Semiconductor, Inc.