external ram in upsd33xx

siksik · ‎2008-05-07

Posted on May 08, 2008 at 05:08

siksik · ‎2011-05-17

Posted on May 17, 2011 at 11:57

Hi,

I want to connect an external ram to a upsd3333 using the pld for latching the address. i used the PA port for the low address bus.

1. Where should i connect the data-bus? to AD[0..7] or to a port?

2. Do i have to use the ALE signal? Can i leave it unconnected?

3. I need a RAM with 17 bit address. Can i use PB port for the high bits

of the address-bus :A[12..16]?

4.Do you have an application-note with a shema of a upsd3333 with

an external RAM?

Thanks,

joseph2399 · ‎2011-05-17

Posted on May 17, 2011 at 11:57

1. D7-D0 of external RAM should be connected to AD7-AD0 on the uPSD.

2. You can configure port A as ''Latched Address Out'', and connect PA7-PA0 to A7-A0 of the external RAM. Please see the attached picture. Connect mcu A11 - mcu A8 to ext. RAM A11-A8.

3. uPSD is 8032 based, a standard 8032 only has 16-bit address bus and can address up to 64K memory when memory paging is NOT used. To address beyond 64K, memory paging must be used. You can use PB3-PB0 and write PLD equations like the example shown in AN1560 (a15_x - a12_x) and connect them to A15 - A12 of your ext. RAM.

4. Sorry we do not have an app. note on this subject.

khtang · ‎2011-05-17

Posted on May 17, 2011 at 11:57

I am using uPSD3422 and I tried to map the PA and PB ports to latched address low and lateched address high as described without success. I do not get any expected address out.

My solution is to define these pins as Combinational logic output, then at the Design Assistant's I/O Logic Equation page I equate these pins to the corresponding adresses, i.e. pa7 = a7, pb7 = a15, etc. I also tie the Output enable pins of these pins to _reset. It seems to work.

Any idea or comment to my solution?

[ This message was edited by: khtang on 08-05-2008 08:40 ]