AT&T 5620 questions

[Jeffrey J Wieland]

I have a couple of questions about the AT&T 5620 terminal:

1.  I tried to upgrade the memory in mine by replacing the 64K ram
    chips the 256K ram chips.  It passes the self test on start up,
    and when I go into cip, cip sees the additional memory (shows
    over 400K free).  However, cip will crash after 10 minutes or
    so.  Tek4014 will crash also.  The errors I get look like the
    following:

    Normal Exception #0x4 at 0x72B379
    Normal Exception #0x2 at 0x0

    Normal exception 4 is "invalid descriptor", which means that 
    there was an attempt to execute an instruction with an invalid
    operand.

    Normal exception 2 is "illegal" opcode.

    It seems that memory errors are ocurring.  I've tried replacing
    the 256K chips -- it doesn't seem to make any difference.  The 
    256K drams are just standard 150 nanosecond parts.

    Do the dip switches on the processor board need to be changed?
    What are they for, anyway?  Maybe someone who has the "5620
    Dot-Mapped Display General Technical Reference" manual could
    tell me this.

2.  What is the parallel i/o port for?  Did anything actually ever
    use it?
--
			    Jeff Wieland
			wieland at ecn.purdue.edu