int e l 1.9 ANSWERS TO A FEW QUESTIONS QUESTION After RESET or power-up, MCS BASIC-52 does not return the proper value for MTOP, what's the problem? ANSWER Virtually every time this problem occurs it is because something is wrong with the decoding circuitry in the system or one or more of the address lines to the RAM are open or shorted. The user should make sure that all of the address lines to the system RAM are connected properly! A simple memory test can be implemented in the COMMAND MODE to verify the addressing to the RAM. First set XBY(1000H) = 55, then walk ones across the address (i.e. P. XBY(1001H) - P. XBY(1002H) - P. XBY(1004H) -- P. XBY(1008H) P.
XBY(1010H)) until all locations are tested. If for instance, P. XBY(1008H) returns a result of 55, then address line 3 (A3) would probably be open or shorted. - 191 -