Datasheet

140 PSoC Designer IDE Guide, Document # 001-42655 Rev *B
A.6 I2C Hot Swapping
Problem: The PSoC does not function independently as a hot swap controller with I2C.
The protection diodes on the GPIO pins attached to the I2C bus load the bus if the
PSoC Vdd is separate from the I2C power supply and is powered down.
Solution: We have a workaround fix. Please find attached block in PDF format.
Figure 1-2. I2C Hot Swapping
Notes:
Place the N channel FETs used in this block so that the source of the FETs
attaches to the PSoC GPIO pin (otherwise the body diodes in the FETs will con-
duct in the same way as the protection diodes).
This drawing illustrates the BSS145 from Infineon, but you may select something
less expensive as long as they are N ch FETs with an RdsON rating for Vgs <=
PSoC Vdd. For example, if PSoC Vdd = 3.5V you need an NCH FET with a spec-
ified Rds ON for a Vgs <= 3.5V (such as the BSS145).
Setting “Pin X” drive mode to “strong” and writing a 1 to the pin Drive Register
enables the PSoC on the I2C bus. Write a 0 to the pin drive register to disable the
I2C.
A.7 Manually Turning off the Analog Section
Problem: For situations where low quiescent current is required, such as sleep, you need to
to shutoff the entire analog section. To completely shut off the analog section of
the PSoC, manually write to the ARF_CR register. You should read about the
ARF_CR register, in the Technical Reference Manual (TRM), before changing this
register.
Solution: To turn off the Analog Section use the following code snippet.
ARF_CR &= ~0x03;
Trace is “grayed out” while in debug mode if no breakpoints are set.
A.8 Trace Issues
Problem: Debug > Trace is grayed out in the title menu of PSoC Designer 4.2 SP2 when in
Debug mode if user is running.
Solution: Set a breakpoint or click Break on the toolbar. This activates the selections in the
drop down menu.
BSS145
100k
PSoC
Pin 1_5
Pin 1_7
Pin X (to enable I2C)
BSS145
I2C SDA
I2C SCL
S
D
G
G
DS