INT 15,43 - Read System Status (convertible only)

	AH = 43h


	on return
	AL = STATUS:

		|7|6|5|4|3|2|1|0|  AL
		 | | | | | | | `---- LCD detached
		 | | | | | | `----- reserved
		 | | | | | `------ RS232/parallel powered on
		 | | | | `------- internal modem powered on
		 | | | `-------- power activated by alarm
		 | | `--------- standby power lost
		 | `---------- external power in use
		 `----------- battery low