STM32MP1 DSI voltage level

[arturo182]

I would like to clear up some confusion regarding the DSI VIO, the stm32mp157a datasheet mentions "1.2 V I/O for DSI interface" but in the EV1 kit the LCD used (the RK055AHD042-CT, for which it's impossible to find a datasheet for, could that be shared too?) uses the RM68200 driver which seems to require 1.8V for IO.

The LCD I would like to use also requires 1.8V so I'm wondering if I need a high-speed voltage translator or will the STM32MP1 support my LCD?

[PatrickF]

All DSI component should use D-PHY signalling levels as stated in the MIPI standard (not public, but you could retrieve some information on various web sites).

As a very simple view, DSI make use of both low-power single ended (1.2V) and high-speed low-voltage differential (about 200mV) signalling, depending DSI is doing control or pixels transmission on the LCD.

STM32MP157 has internal regulators to create voltages required by the DSI D-PHY (e.g. VDD1V2_DSI_REG).

RM68200 as well has internal regulator(s) to generates DSI D-PHY voltages from its supplies.

Goal of MIPI DSI standard (using D-PHY interface) is to simplify and ensure electrical compatibility.

So, in addition to a common VSS, DSI signals pairs must be connected directly between the STM32MP157 and any DSI serial interface compliant display controller (no need of level translators).

You obviously need to check your LCD spec about the number of data lanes (STM32MP157 has up to 2 data lanes) and maximum data rate (STM32MP157 supports up to 1Gbps per lane).

[arturo182]

Thank you for the exhaustive explanation Patrick, but I'm still a but unsure if that means that my LCD can be used with the STM32MP1, since like you mention the 1.2V voltage and my LCD's datasheet mentions 1.8V:

As for the data lanes, the LCD uses 2 and the MPU has 2 so that part should be fine.

[arturo182]

Sorry seems the image upload failed.

[PatrickF]

If the LCD datasheet mention DSI serial interface, it should work, I assume their bullet about 1.8V supply for DSI is not giving details on their internal LDO or else.

I will not worry too much for that as. There is no rationale for an LCD maker not to comply with the standard everybody uses.

This is similar for other interfaces using complex PHY, like USB high-speed, which uses many local supplies, but in the 'wires' both end comply with same standard for full interoperability.

Could you share the reference of the LCD panel and display controller you plan to use ?

[arturo182]

Thank you, that seems reasonable :)

As my profile mentions, I am a hobbyist so the LCD I want to use is a Blackberry Q5 LCD (marking LCD–49754-000) obtained from China as a replacement, the datasheet is not officially public, although it is possible to find it online, but it is marked as confidential so I wouldn't want to risk legal issues by posting it here.

[SHart.5]

This application provides information on how to interface STM32MP1 Series with a MIPI CSI-2 camera. The STM32MP1 Series,

like the STM32 high-performance MCUs can address CMOS camera sensors through its DCMI (digital camera module

interface) parallel port. However, it is possible to extend the range of addressable camera sensors for instance MIPI® CSI-2

cameras (camera serial interface), thanks to the STMIPID02 MIPI CSI-2 deserializer discrete component.

The MIPI CSI-2 interface protocol has become for many years the standard technology in today’s embedded sensors, mostly

driven by the mobile market and it is also widely used in the industrial market where MIPI CSI-2 brings decisive advantages,

offering a lower pin count and cost versus the conventional parallel interface or MIPI CPI.

The STMIPID02 MIPI CSI-2 deserializer can address a broad range of MIPI CSI-2 camera sensors used in mobile devices and

automotive applications. This direct interface removes the requirement for as sociated software overhead linked to frame

decoding (for camera over USB or Ethernet for instance).

The purpose of this application note is to demonstrate, using the DH96 Avenger board, the STM32MP1 Series capability to

address the 5 Mpixel OV5640 MIPI CSI-2 camera sensor through the STMIPID02 MIPI CSI-2 deserializer. Both drivers are

available and included in the STMicroelectronics OpenSTLinux software distribution package. For the purpose of this application

note and according to the STMIPID02 deserializer specifications, the focus is made exclusively on the MIPI CSI-2.1 protocol

over a D-PHY