HP 5501A Operating And Service Manual page 111

There is a 36-bit data register on the binary interface card: 28 bits are used for binary data, four
bits are used a s a decimal point location buffer, and four bits are used a s error status buffers.
This register has two separate tri-state I/O ports, one for backplane input/output, and one
for controller input/output.
When an instruction is received from the backplane to transfer data to or from the controller,
the control logic switches to the data mode. In the case of data input from the controller, the
data register i s sequenced by the control logic so that each time valid data is available, that
data i s clocked into part of the data register. If the card has been set (jumper selectable) for
16-bit words, the first 16 bits of data are loaded into the upper bits of the register with the four
most-significant bits being the decimal point location code. The next 16-bit word is loaded into
the remaining half of the data register and the control logic immediately switches back to the
command mode (error status bits cannot be loaded from the controller). If the card has been
set for 8-bit words, the first word is placed in the upper portion of the data register and again
the four most-significant bits are the decimal point location. Then three more data words are
accepted and placed in successively lower bit locations with the last word in the least-signifi-
cant eight bits. The control logic switches immediately back to the command mode after the
fourth word.
If data i s to be sent to the controller, the sequence i s the same except that the control logic
sequences the data register to put data onto the interface lines, most-significant word first.
If an error has been detected, the upper four bits (decimal point bits) of the transmitted data
contain all ones to indicate that an error is being transmitted and the four status bits replace
the data in the next four bits. This allows the same sequence to be used for error transmission
a s for regular data transmission.
A jumper-selectable data-mode-only configuration causes the binary interface to ignore
commands from the controller. It will still transfer data, however, so it can be used a s an I/O
device for some peripheral other than the system controller. For additional information and
schematics, refer to the 10746A Binary Interface Operating and Service Manual.
3.16 10760A Counter
The 10760A Counter is a general-purpose counter consisting of line drivers and receivers, a
resolution extender, a pulse converter, and a reversible counter (see Figure 3-13).
and Control
Loaic
esolution
!
Extender
I
Error
1
DetectO
12.6 MHI
Clock
self Test
Valid Complete Backplane Data Bus
28-Bit I
Asvnchronous Counter
Figure 3-13. 70760A Counter Block Diagram