determine the status of the cmdrd signal therefore by reading status register 645 control circuit 501 is able to know or is provided with an indication from microprocessor 601 that command code has been set in polling command register 643 when control circuit 501 observes the cmdrd flag bit d 3 of status register 645 and finds that an instruction or command has been placed in register 643 it reads the contents of command register 643 during a normal read cycle that is it reads the command sent from microprocessor 601 the commands are for instance to start transferring print data to data transfer controller 603 to start printing or to display messages on console 518 as shown in fig2 when control circuit 501 reads the contents of polling register 643 cmdrd output by flip flop 643 c its output is then reset high using the poll signal therefore by observing a bit d 2 of transfer flag register 647 microprocessor 601 is able to know whether or not the command it output was read or received by control circuit 501 in addition to the data described above which shows whether or not a command has been placed in the register by microprocessor 601 status register 645 also retains the data illustrated in fig2 which is described as follows bit d 0 of this data is set low by the ewrdy signal which is generated within read control circuit 620 when data is written there by control circuit 501 discussed later when that data is read by.