The price of true 16 bit memory devices has fallen to such an extent that is now feasible to use them in even cost-sensitive applications. The use of 16-bit AMD FLASH EPROMs like 29F400 has already become commonplace.

Now, the IDT71016 16-bit RAM from Integrated Device Technologies allows the easy addition of word-wide RAM to C166 and C167 systems. There are a few points to be aware of when using these devices:

The C167's /BHE goes to the 71016's /BHE (Byte high enable)
The C167's A0 goes to the 71016's /BHE (Byte low enable)
The C167's /WR goes to the 71016's /WR
The C167's A1 goes to the A0 on the 71016

This last point is often missed and can result in the need for a lot of track cutting and mod wire! The reason that A1 goes to A0 is that the RAM is arranged word-wise so each increment of the address is in fact two bytes. In turn, the 167 always reads byte data as words, discarding the unwanted byte during 8-bit accesses. Thus A0 is effectively redundant as an address line. It is worth noting that during byte writes, the data to be written appears on both the high and low order datat lines. The distinction between upper and lower bytes in a word address write is made by the /BHE and C167's A0 being routed to the /BLE.

For more examples of interfacing C167 devices to ROM and RAM, please see our "Insider's Guide To Planning 166 Family Designs"