since the pic18f’s can address external ram and cc5x can handle external ram do you think someday you could have a development board with it?
Really? I had no idea. Will look into it…
How much RAM you lookin’ for?
Correct me if I’m wrong but the 18F is not setup to directly access an external RAM meaning that it does not have separate address and data lines. The 40 pin versions have enough I/O to allow for a software RAM controller. You could use 16 pins for address (65KB RAM) and 16 more for data and 1 for address enable or you could use 24 pins for addres (16MB RAM) and 8 more for data and 1 for address enable.
Perhaps you were reading the datasheet for the 18F and saw the part that says:
“Linear program memory addressing to 32 Kbytes”
“Linear data memory addressing to 1.5 Kbytes”
Those two lines refer to the PIC’s internal memory, not an external source.
If one looks at some of the higher end 64 and 80 pin packaged 18f series pics, they do support external ram. I would love to get ahold of one of these myself. Is why I just bout the atmega128 mini header unit, for the external ram interface.
Ray Moore
Lead Tech
NetHarmonix, Inc.
At the time of my last post in this thread, I wasn’t aware of the PICs that could use external memory. Since I discovered them, I have been looking for a way to use one. The packaging of the devices is very small with extremely fine pitch pins. I could not find an adapter for them anywhere so I would have to have a board printed just to prototype with one.
-Bill
Hi,
I used a couple of octal latches (74HCT573) to interface a 128K x 8 external SRAM to a PIC16F877.
I used the Port D to first write the High address to the high latch, and then the low address to the low latch.
I used 3 more port lines for read, write an output enable plus a couple of lines for the strobe lines for the address latches - and I needed A16 to acces the top half of the RAM
Port B was used to get the data in and out of the RAM - but you could always use Port D to save a whole 8 bit port.
I wrote some very simple drivers in asm and managed to get the RAM to store 8 seconds of speech and play back through a R-2R ladder network to an amplifier and loudspeaker.
Since then I have found an interface for a Compact flash to PIC16F877 interface - so you can have 256Mbytes or more accessible to the PIC.
Another neat idea is to use an 8 pin serial flash ram such as the ST M25P80 (8 Mbit) - connected to the PIC through the SPI bus. These are very quick devices and ideal for storing natural voice prompts etc.
I will try and look out the schematics for the PIC to SRAM interface.
Ken
hi!
i am using PIC18F452 with K6T1008C2E RAM. i am writing to ram then reading and saving the read sample in compact flash card. i am getting problem with address locations. some addresses are giving garbage while some are giving correct sample. can you help how to locate addresses. address lines are connected to PORTB and PORTD of microcontroller (lower pins to PORTD) and A16 to RC5, data lines are also conncted to PORTD, for this using Dlatch. for example
RC5=0;
PORTB=0x08;
PORTD=0x01;
this is how i am addressing and this gives ok result. but doing
PORTB =0x07; or less or 0x10 to 0x17 or 0xFE; giving garbage
please help
thanks