INPUT/OUTPUT (continued)


Mass Storage (cassette or disk) flag useage:

When a file is opened, the zero flag in the 8080
CPU is set upon entering the mass storage output routine.
When a file is closed, the carry flag in the 8080
CPU is set upon entering the mass storage output routine.
If the carry flag is set upon returning from a mass storage
input routine, it is an indication to the BASIC interpreter
than an error has occured on a read operation.


Console (CRT, teletype, etc) flag usage:

When an input routine is entered with the zero flag set,
it is a check for control-C or control-S, rather than an
actual keyboard read operation.  If a control-C was pressed
on the keyboard, a return is made with the zero flag set.


The Terminal (TRMNL) Table:

This is a table located in the scratch area above BASIC.
There are ten entries, with three bytes per entry, each
entry corresponding to one of the ten I/O channels defined
by the CHANL table.  The first byte of each entry is the
terminal width, that is, the number of characters after
which there is a carriage-return issued.  The second byte
is the current terminal position.  The third byte is used
to determine the rubout.  The low 7 bits of the byte is
the code which is sent to the terminal when a 7F(hex) is
received from the keyboard.  If the upper bit is 0, the
internal pointer is not decremented.  If it is 1, it is.


The KIND byte:

This is a byte located in the scratch area above BASIC.
It is set every time any mass storage (cassette or disk)
operation is invoked.  It's purpose is to make available
to the I/O section information about the kind of transfer
being made.  Only the low 5 bits are currently used.

Content	Statement		Bit	If 0	If 1
   0	LOAD			 0	input	output
   1	SAVE			 1	ASCII	binary
   2	BLOAD			 2	program	data
   3	BSAVE			 3  not append	append
   4	GET			 4  not opn/cls  open/close
   5	PUT
   6	BGET
   7	BPUT
   8	APPEND
   20	OPEN
   21	CLOSE


				E-2