RCONN@SIMTEL20.ARPA (Rick Conn) (08/14/85)
Hi, Ron, I'm afraid your rumors are true. The 64180 has an on-chip MMU which provides the memory management. This is accessed via on-chip I/O ports and the special set of 64180 I/O instructions. I haven't found this to be a problem yet. SW-wise, you init the MMU, defining the 64K memory banks to have 0, 1, or 2 common banks (common to all memory 64K memory banks) and 1 base bank (unique to each 64K memory bank). Switching banks is like loading a segment register, wherein you output any of the standard registers or (HL) to the MMU for the selection. The resolution of the common and base banks is to 4K, but that does not stop you from having a 63K+ TPA. I really like the 64180, but a problem came up last night which really bothered me. One of the two UARTS onchip (which I am using to connect to a Smartmodem) pays attention to the DCD line. You can sense this line internally thru a port. However, if DCD drops off (no carrier), then the Transmitter section of the UART is disabled! Ban news! No more comm to the Smartmodem for dialing the phone, answering the phone, hanging up the phone, etc. You can, of course, set the switch on the Smartmodem to keep DCD true (reverse logic, so 0 actually), but then you can't use DCD to detect loss of user signal. There is a way around this problem for the Ciarcia board, but I can't talk until Nov or so for reasons of confidence. Ciarcia will have a project on this option in Dec Byte. If Steve says I can talk earlier, I will. Rick -------