12
there is a time difference between when common memory data is set and when
I/O data is set. This time difference must be taken into consideration when pre-
paring both the ASCII Unit and PC programs.
1 cycle
MOV(21/030) WRIT(87/191)
I/O refresh
Output data set
Data set in common
memory
With WRIT(87/191)
time
The following diagram illustrates the various timing relationships between the
PC and ASCII Unit during data transfer.
Relationship between READ and WRITE Timing
PC busy: n (00)
Write/Read data: n or n+1
PC write complete: n (01)
PC read complete: n (02)
ASCII busy n+1 (00)
ASCII read complete: n+1 (01)
Read data
PC Unit
↔
common memory
common memory
→
ASCII
Write data
ASCII
→
common memory
ASCII write complete: n+1 (02)
PC WRITE
PC READ
PC
→
ASCII
ASCII
→
PC
PC READ
PC WRITE
Application Program
BASIC Program
Relationship between Output and Input Timing
Output data
PC
→
ASCII: n (08 to 15)
Input data
ASCII
→
PC: n+1 (08 to 15)
I/O refresh
PC
→
ASCII
ASCII
→
PC
PC
→
ASCII
ASCII
→
PC
2-2-2 Four-Word Configuration
In four-word mode, WRIT(87/191) and READ(88/190) instructions cannot be
used. The ASCII Unit can be set to four-word mode by setting pin 5 of the front
panel DIP switch to ON.
Bit Allocation
The following two tables identify the individual bits in the four words allocated to
the ASCII Unit. Notice that words n and n+1 are used for output and words n+2
Data Configuration
Summary of Contents for C500-ASC04
Page 1: ...C500 ASC04 ASCII Unit Operation Manual Revised February 2001 ...
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