Screen Device Specification

Memory Layout

Byte Mode Name Description
00 R X error indicator
01-02 R - zero
03 R Y character count
04-06 R - zero
07 RW Z character


The program will contact the motherboard at [host:]port and register itself with the given address and interrupt. Then, the program will be ready to receive bytes and display them. Under Unix a Byte is displayed by sending it to the standard output. Whenever ready to receive a byte, it will signal an interrupt with the given interrupt number. At the given address it will provide a read/write octabyte in the format: given above.

The X byte signals errors. It will be 0x80 if an error occured and 0x00 otherwise. By setting the sign bit errors can be easily checked..

The Y byte contains the number of characters that were written to this address since the last output. This should be 0 if the address is ready to receive a character or 1 if the hardware is bussy with writing a byte. Any other value will indicate that characters were lost since the last write operation.

The Z byte contains the last character received. It is valid only if YY is not zero.

The complete ocatbyte will be reset to zero after a byte is output..


The Screen has the following configurable parameters:
host localhost the host where the bus is located
port 9002 the port where the bus is located
address default address where the resource is located
interrupt not set interrupt sent when ready
x 0the x position of the window
y 0the y position of the window
minimized falsestart with a minimized window
debug falseto generate debug output
debugmask 0xFFF0 set mask to hide debug output
verbose falsemake debugging verbose, sets debug mask to zero
define not setto define a name for conditionals
config not setfilename for a configuration file
help falseto print information

These can be set in default.vmb