On Thu, 12 Mar 1998 15:30:27 +1300 Gavin Jackson writes: >Hi there PIC'ers > >I have an old TX motherboard with quite a few >DRAM chips on it which I could use in latter >projects for storing data. I was wondering if there >is anyone who could help me with the pin-outs. The pin-out is: 1 - NC * 16 - Vss (ground) 2 - Din 15 - CAS 3 - WE 14 - D out 4 - RAS 13 - A6 5 - A0 12 - A3 6 - A2 11 - A4 7 - A1 10 - A5 8 - Vcc 9 - A7 * On a few 64K DRAMS, pin 1 controls a refresh function. I think it is generally OK to leave it open. On 256K DRAMs, pin 1 is the highest address. Notice carefully that Vcc is supplied to pin 8, and pin 16 is ground. This is the reverse of most 16-pin logic chips. It is a holdover from older DRAMs which required 3 power supplies, one to each corner pin. I don't think there are any 64K ones which require power to pin 1. Be sure to connect a 0.05 - 0.22 uF capacitor between Vdd and Vss right at the DRAM chip. They draw nasty surges of current. Of course, you can connect the address bits to your circuit in any order. The data will be recalled from the address where it was stored. All pins except Dout are input-only. The Dout pin is tri-state. The RAS, CAS, and WE pins are active low. When the chip is idle, they should be high. For bit-banging a DRAM with a PIC, the following will be sufficient: READ/REFRESH CYCLE: Apply 8 bit row address to address pins. Pull RAS low (If this is a refresh only cycle, return RAS high now.) Change the address to the column address (the other 8 bits of a complete 16-bit address) Pull CAS low Read data from Dout. Return RAS and CAS high. WRITE CYCLE: Apply 8-bit row address Pull RAS low Pull WE low (OK to do at the same time as RAS) Apply column address and setup data on Din Pull CAS low Return RAS, CAS, and WE high. In order to keep the data alive in the RAM, you need to apply row address/pull RAS low with every row that is in use at least once every 2 or 4 ms. (Generally, at room temperature, much less frequent refreshing is possible, but out of spec). These refresh operations can be part of normal read or write cycles or just RAS-only refresh cycles. Most all 64K chips also support read-modify-write cycles and page mode operation. These can wait until you get the two cycles above working. _____________________________________________________________________ You don't need to buy Internet access to use free Internet e-mail. Get completely free e-mail from Juno at http://www.juno.com Or call Juno at (800) 654-JUNO [654-5866]