RCA 301, Programmer'S Reference Manual

Page: 187 / 235

8 W rite Normal (TWN)
General Description
This instruction writes a series of consecutive characters from HSM to a magnetic card on a 3488 unit, starting
at the block previously selected by the Select instruction. Transfer of information ends when the last character in the
specified HSM area is written or after the last character of block 255 is written, whichever occurs first.
Format
Operation — 8
N — Specifies device number.
(60)
s
to (63)
8
t>
n
Model 380-14 channel.
(64)
8
to (67)
8
on Model 380-24 channel.
A Address — Address of the HSM location of the first character to be written. Block must be previously selected
by Select instruction. Must be an even address.
B Address — Address of the HSM location of the next to last character to be written. Must be an even address.
Outline of Operation
If all conditions are acceptable, the write begins when the 3488 unit indicates that the beginning of the selected
block has been reached. Character transfer ends on A-B Equality or when the end of block 255 is reached, whichever
occurs first. The Block Address Register in the 3488 unit counts up with each block written.
If A-B Equality is not obtained by the completion of the write of the last block of the band, the block address is
incremented by one and, if necessary, the heads are repositioned. When this occurs, the instruction is not terminated.
The write continues when the next block is in position under the read-write heads.
When A-B Equality is reached, the Write instruction is terminated and the mode is freed. If the write is not in
full block multiples, the remainder of the last block is filled with spaces. Note that the mode becomes free prior to
the completion of the read-after-write check. This is true even when the A-B Equality is reached on the 650th character
of the last block. Because of this, the Input/Output Sense for a read-after-write error can not follow a Write instruction;
it must always be preceded by an Input/Output Sense (Test for Read or Write busy) to ensure that the unit is no longer
writing. This test is set when the write is issued; it is reset when the read-after-write check is complete for the 650th
character of the
last block.
Whether the card stays on or leaves the capstan after a write is terminated is under control of the Select instruction.
When a read-after-write error is detected, the following occurs:
1. The write terminates immediately.
2. The read-after-urrite error indicator is set.
3. The Normal Mode and channel are freed.
4. The
test for read or write busy indicator is reset.
5. The card remains on the capstan.
6. A Block Preselect, if any, is executed.
When a write is illogically issued following either an
unconditional card removal or a conditional card removal,
the instruction remains staticized until a card reaches the capstan or the unit goes inoperable.
A Write instruction can be issued anytime after executing a Card Select, or after a legitimate Block Select. The
Normal Mode remains busy while the instruction is waiting to be executed. The channel allows only one (read or)
write at a time. Two channels allow two (reads or) writes (or read and write) simultaneously.
Final Register Contents
(A), = Address of HSM location one to the right of the last character transferred.
(B)t = (B)i
XV-7