the serial is being sent from a computer, at the moment it is from Hyper terminal but in the future it will be a custom application.
also in the final version this will be driven with RS232, where as at the moment i am using the FTDI chip from the arduino board.
i am not sure how i would try software serial on a 328? the board has the FTDI chip hard wired to TX and RX, at the moment i am using the board with the chip removed just as a serial converter to drive the ATtiny. if i use the original 328, won't the hard wired tx and rx pins automatically interrupt the processor even if i jump those pins over to a software serial port?
i am sure the ATtiny is using the external resonator because it doesn't respond if i disconnect it, but it may be that the resonator is not accurate enough, maybe it needs a real crystal...
thanks for the replies everyone
just as a note, i think i have worked out a fix to solve my problem. instead of asking the ATtiny to transmit on receiving serial and expect it to transmit at regular enough intervals, i am going to get it to transmit on receiving a single serial command and repeat that command until it receives a stop command. it might not work because if the ATtiny misses that stop command it could be transmitting for ever. i can put a limit in to maybe stop after 16 transmissions, but still it may not work