HP 13255 Technical Information page 21

13255
Cartridge Tape Module
13255-91032/19
Rev AUG-Ol-16
The variable modulus counter consists of two counters. One is an a-bit
counter
(U213
and
U214)
which counts from a base state to the overflow
state (which generates a carrY output); the second is an 8-bit Up-down
counter which contains the value of the base state. The up-down coun-
ter Is loaded with the two's complement of the desired modulus. In
Record mode, the
up-do~n
counter is reset (U311, Pin 11 and U313, Pin
11)
to the two's complement of
115
octal
(77
decimal) giving a carry
output at
N
77
nominal biphase
all period
------ microsecond
= ------
microsecond
= ---------------
4.9150 4.9150
8
In Read mOde, the up-down counter is initialized to the same value.
Then, based on tne actual frequency of the phase/data transitions, the
up-down counter is incremented or decremented. (Note that incrementing
the up-down counter decrements the modulus ot the counter.)
The cell decode counter is decoded as follows when 1n Record mode.
U212, Pins
A
B
C
0
CIN f"UNCTION
-~-----------~--------------I----------------
t
o o
1 1
Phase Position
1
1
o
1 1
Data Position
When in Read mode, the cell decode counter appears as follows.
Initialize State
Decrement
N
Increment
N
Decrement
N
Increment
N
A
U212, Pins
B C D FUNCTION
---------------~------ -----------------~
0
1 1
0 1 1
1 0 0
1 0 0
1
0
t
1
0
1
1 1 0
1 1 0
1 1 1
1
1 1
0
1
0
1
0
1
0
1
0
1
}
}
}
}
}
}
}
)
}
)
Illegal Zone
For Transitions
Zone For Phase
Transitions
Zone For Data
Transitions