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3803 MODEL 3 AND 3803 MODEL 1 DIFFERENCES
The Model 3 was designed to attach to 370/ 115s and 125s.
It
is basically a Modell with
three major differences. These differences are required because the 115 and 125 don't
use a standard 370 channel.
- ALUI is modified to interface with the channel on the 115 and 125 and translate the
activity to 370 channel sequences which the rest of the 3803 understands.
- Hardware logic called AUTO DATA TRANSFER is provided to handle the data trans-
fer.
It
includes the byte counter.
- A 32-BYTE DATA BUFFER is provided for reading and writing. This large a buffet
is required in the event that data crosses a page boundary. When this happens, time
is required for ALUI to set the address of the new page back into the data address con-
trol in the 115 or 125.
The 3803 Model 3 tape subsystem connects to the Magnetic Tape Adaptor (MT A) inter-
face of system 3115 or system 3125. The term MT A interface refers to a set of lines over
which control and data signals are exchanged between the control unit and the MT A
portion of the system.
The basic 3803-3 Control Unit consists of a MT A interface attachment section, a data
buffer section, a microprogram section, a read section, a write section, a tape unit inter-
face and a CE section.
I/O commands received from CPU through MTA are executed with microprograms resi-
dent in two independent read-only storage (ROS) units within the 3803-3 Control Unit.
One ROS controls the MTA interface lines while the other ROS controls the tape unit
interface.
The 3803-3 Control Unit operates in burst mode for all data transfers and executes com-
mands received across the interface, performing one command on a single tape unit at a
time.
When a 3803 Mode13 is taken offline, all functions from the control to the tape unit
become the same as a Modell 3803.
3
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