HP 13255 Technical Information page 19

1325S
Cartridge Tape MOdule
13255 ..
91032/17
Rev
AUG-Ol-76
Two versions of the Run command are contained in the command register
(UI5).
SPUN (Servo ~un) is generated at
U24,
Pin
8
to enable the tape
motion decoder (UI6). SFUN is cleared if the hole
ed~e
detector (U23,
Pin 12) detects a transition into a hole. IRUN (Interface Run) is gen-
erated at
U24, Pin 6
to enable the slow torward tape motion decoder at
U36,
Pin
8
which generates
ISF
(used only by the encoder/decoder
logic). This prevents a discontinuity in encoded or decoded data when
movinq across a holp.. Bottl SRUN and IRUN are cleared after a system
reset.
The SRUN, FORWARD, and FAST Signals are translated in this block into
the signals SREV (slow reverse), SFO (slow forward), FREV (fast re-
verse), and FFO (fast forward) wnich are used by the servo electron1cs
on the Read/Write PCA.
The CLRINT signal is generated for the interrupt logic by U27, Pin 8
when the processor performs a status request, enablinq the STATUS
EN
signal.
The CLRINT signal is present for one cycle of SYS eLK after
STATUS
EN
goes low.
3.0.1 DATA PATH CONTROL - CTU INTERFACE PCA.
3.0.3.1
The data path control circuitry transfers data to and from the terminal
bUS.
It also converts serial bits from the tape into bytes and con-
verts bytes tram the terminal bus into serial bits.
3.0.3.2
The data 1/0 buffer (U13 and U33) is an 8-bit register with a 2-port
input multiplexer. It provides one byte of butfering between the ter-
minal bUS and the serial data register.
3.0.31.3
In Record mOde, the data is loaded into the data
I/O
buffer from the
terminal bus, enabled by RO/WFT SELECT being low. (Note that the data
buffer is loaded with complement data since it is loaded from the
ground true terminal bus.) The data byte is loaded into the serial
data register after the previous byte has been encoded. The serial
data register is then shifted right (via REC DATA) into the encoder at
mid cell point (data transition position) and the encoder is comple-
mented at end cell point (phase position).
3.0.31.4 In Read mOde, the serial biphase data is read into the transition
detector (U28, Pin 14) ot the encoder/decoder logic and shifted into