topic Re: LPC18xxJET100 - SDRAM DQM Signal missing? in LPC Microcontrollers

LPC18xxJET100 - SDRAM DQM Signal missing?

urosg — Wed, 25 Aug 2021 11:12:08 GMT

I am working on a new design where I would like to use external SDRAM memory with the LPC1833JET100 (TFBGA100 package) part because we already use it in our other products, but all without external RAM.

While preparing schematics and going through signals I am missing a EMC_DQMOUT[0:3] signal on the TFBA100 package, is there a way to repurpose OE signal for example for this function as OE signal is not used in SDRAM configuration only in SRAM configurations.

Since there is a missing DQM signal is it even possible to use SDRAM with LPC18xx in TFBGA100 package or am I stuck with SRAM only?

Thanks for any insight!

Re: LPC18xxJET100 - SDRAM DQM Signal missing?

xiangjun_rong — Thu, 26 Aug 2021 06:23:04 GMT

As you know that the EMC_DQM[0:3] are output signals from EMC module of LPC, they are used to select Byte lane of SDRAM.

For your current design, can you tell us the data width of SDRAM, if you use 8 bits data width, you do not need connect the DQM signal, if you use 16/32 data width, how do you connect the DQM pins of SDRAM at the time being?

XiangJun Rong

Re: LPC18xxJET100 - SDRAM DQM Signal missing?

urosg — Thu, 26 Aug 2021 19:41:48 GMT

The design in question would be using an 8bit wide data bus, but the SDRAM chip still has the DQM signal, which if I understand correctly affects write/read operations.

SDRAM Part Zentel A3V56S30GTP-60

Re: LPC18xxJET100 - SDRAM DQM Signal missing?

xiangjun_rong — Fri, 27 Aug 2021 03:21:39 GMT

Hi,

I see your issue, the EMC module of LPC18xxJET100 with 100 pins does not have DQM pin, but the DQM function is required for the Zentel A3V56S30GTP-60 SDRAM, so I do not think the DQM pin of SDRAM can be connected to a fixed logic. So I do not think you can connect SDRAM because of lack of DQM pin for the LPC18xxJET100 .

Hope it can help you

XiangJun Rong