diagnostic procedures furthermore the aforementioned common 256 byte ram area 110 discussed with regard to fig1 for the engine control communication is resident at the top of the 64k memory area this portion of memory is shared by the engine control board 54 and the bit map cpu 56 for communication therebetween in operation the 32k system rom provides a jump to the 4k loader program 108 upon a power up sequence at that time if hardware problems are detected the present invention provides a corresponding error signal explained below to the host computer an error regarding the hardware structure would typically be a fatal error and the system operation would be inhibited the printer process controller according to the present invention communicates with the front panel 70 illustrated in fig4 under an error condition the fault light 122 lights up or the corresponding error code is indicated in the two digit indicator lights 124 if the error is a recoverable error denoted on the front panel can be corrected by operator intervention or host computer reset signals the operation of the front panel 70 reverts to normal operation when the data output device according to the present invention is initially powered the power up sequence invokes the top 4k loader which includes some error handling processes the top 4k loader then loads the system in the bottom 32k area of the system ram 100 and removes the system memory area during normal operation during a fatal error condition the 4k loader at 108.