Looks like a red-herring to me, Erik. The DS89C450 is a one-clocker.

I can see how you'd do the bits, simply by using RRC and MOV TXD,C multiple times, with the clock toggle, the byte fetch from XRAM, and the DPTR maintenance interleaved along with the loop control. That's all first-year MCU 101 stuff. I don't see how you find time to process the interupt, though, particularly if you have to receive the data to refill your 5000-bit, or whatever, XRAM buffer at some point. You're the one who brought this tightly timed process up. I merely said that there are times when it's reasonable and convenient to use the 82C55 with a cycle stretch via the external bus. You simply denied that and bring up this otherwise irrelevant case.

I'm not the least bit interested in how you produce your bitstream, but I am concerned that you're constantly avoiding the real subject. Nobody cares about your display driver code. However, playing fast and loose with the details, resulting in claims you can't support, is a concern. If you're reckless with the numbers, you get caught. You opened the door to the question of how one can transmit an uniterrupted bit stream at 5000 bits per half-millisecond, or 10 Mbps,

I pointed out that there is at least one case in which the 82C55, slow as it may be, is fast enough that its cycle-stretching requirement wouldn't slow down overall system performance by even a teensy amount. I've never denied that there are applications where it would not fit. That component is too slow for some of my applications, too, aside from the fact that I don't really like it.

You simply can't deny that there are places where it works very well. It just doesn't work in ALL cases.

Your inane and infantile remark, some time back, about "stomp your feet, refuse ..." when directed to use a given component, is just as unrealistic as the assertion that there are no applications where this component might fit. It's not appropriate to encourage students to refuse to do their homework, either. I agree that WE shouldn't do it, but it's not because of the 82C55.

RE