Coldfire V1 & VUSB33

[Eric_t]

Hi everybody

I am going to start my first project with Coldfire v1 (MCF51MM128).

I will not use USB, but I am not sure where VUSB33 should be connected.

Should I connected it to 3.3V ?

Thanks

Nikos 

[TomE]

Referring to the Reference manual:

2.6.2 Recommended System Connections

This diagram shows a 0.1uF capacitor on this pin, and no other connection.

2.6.4 Power
VDD1,2,3 and VSS1,2,3 are the primary power supply pins...VUSB33 maintains an output voltage of 3.3 V and sources enoughcurrent for the internal USB transceiver and USB pullup resistor.The VBUS input is used to supply the voltage necessary to powerthe internal USB 3.3V regulator. VUSB33 can also supply theinternal USB when there is no VBUS supply and the internal USBregulator is disabled.For VUSB33, two separate capacitors (4.7 uF bulk electrolyticstability capacitor and 0.47 uF ceramic bypass capacitors)must be connected across this pin to ground to decrease theoutput ripple of this voltage regulator when it is enabled.

Table 3-4. Low-Power Mode Behavior (Continued)USB 3.3V Regulator | Off | Optionally On [7] | Optionally On [7]Note 7: USBVREN in USBTRC0 is set to enable USB 3.3V Regulator, else off

27.6.1.26 USB Transceiver and Regulator Control Register 0 (USBTRC0)

USBVREN
USB voltage regulator enable bit. This bit enables the on-chip 3.3V USB voltage regulator.
0 On-chip USB voltage regulator is disabled (OFF MODE)
1 On-chip USB voltage regulator is enabled for Active or Standby mode

Tom

[Eric_t]

Thanks Tom for the responce.

I had read the manual of MCF51MM128 before my post and I knew that pin VUSB33 needs only a 0.1uF capacitor.

I am just wondering what happens when the USB module is not used.

For example on PIC32, VUSB is USB internal transceiver supply and if the USB
module is not used, this pin must be connected to 3.3V.

I was wondering if a similar connection should be on  MCF51MM128 when the USB module is not used.

I have searched the manual of  MCF51MM128 but I couldn't find anything.

Thanks

Nikos 

[TomE]

In your original question it was not clear that you had already done some research, so I "answered the wrong question".

The chip is designed so it can be put into various low power states, with peripherals powered down or disabled or not clocked. If some of those states will work with the USB powered down then they may all do.

The best answer to any hardware questions with Freescale chips is to look to consider the development boards to be "definitive references". If a pin isn't documented well in the Reference manual, then make sure you copy how it is connected in the Development Board. If it isn't connected to a power rail there then it probably doesn't need to be. If there is a jumper or switch to allow an optional connection, then make sure you add that feature to your board in case you need it.

In your case I'd add a jumper or pads that can take a zero-ohm resistor to 3V3, just in case.

There are also cases where the development boards seem to disobey statements in the manuals. Refer to:

https://community.freescale.com/message/85518#85518

Read through the above and follow the reference to "Bear Pit" to learn more about how to read the manuals.

Tom

[Eric_t]

Thanks TomE for your help.

I wil add pads that can take a zero-ohm resistor to 3V3.

Nikos