Morning All, I've kind of designed myself into a corner using 5 74HC461 into a DMA transfer function. I used these chips initially as they offloaded alot of the mundane address HSB-LSB latching overhead from the 87c52 only to find the HC/HCT version of this chip was never released. The PCB art is done ready for making, software is done, yada yada so I'm trying not to have a drastic redesign slap in the face. What surprises me is there are no CMOS 8 BIT UP COUNTERS WITH PRELOAD AND TRISTATE OUTPUTS's. So I'm looking at a 24pin skinny PIC doing the job. Or its daughter board time. The PCB doesn't have room for 74c161s so a redesign of the board requires use of the existing real estate. Now,can the ports of the pic be put into a high impedance mode like on the 8051's? A(sudo tristate)
You should be able to do this with a GAL22V10 - or, at least, the Atmel ATF22V10 as Lattice no longer make their version. Here's the pinout of the 74LS461...
...and here's the ATF22V10:
The macrocell for the 22V10 looks like this...
...so you can use pin 13 as an OE for the outputs you want. If you need the Carry In function on pin 23 that will have its output disabled.
Depending which speed version you get, you can run at maximum clock frequencies of 80Mhz to 166MHz. The only possible downside is that it needs a 5V supply, where a 74HC, it it existed, would have been able to run off 3.3 if you'd needed it to.
The 16F873 has 28 pins so that can't occupy the same footprint, though it's not too much bigger. I'm pretty sure there aren't any 24 pin PICs.