Local Storage
The local storage is 128 bytes long (64 halfwords) addressed by byte or by halfword. It is organized in 16
blocks (or pages) of eight local storage registers (LSRs), each of them being one-byte long, used to store
the microcode pointers, the cycle steal and command queue control blocks, the program status words, and
working register.
The local storage registers can be displayed or altered from the operator console, using the TSS func-
tions.
Read-Only Storage
The read-only storage (ROS) is 8K bytes long (4K halfwords) addressed by halfwords. It includes all the
permanent code needed to IML or dump the microcode and to perform diagnostics.
The ROS can be displayed from the operator console, using the TSS functions.
Control Storage
The control storage is 64K halfwords long addressed by halfword.
In each module, an error checking and correction (ECC) mechanism detects and corrects the single or
double bit errors (soft or hard) of that module.
When an unrecoverable double error is detected, register X'03' bit 1 is set ON, a hardstop condition is
raised, and two data bytes with parity are sent to the CCU.
The control storage is used to store:
The scanner microcode.
The buffers for the transmitted and received data, and the line control blocks and parameters.
Tables and service buffers.
The control storage can be displayed or altered from the operator console, using the TSS functions.
CSP External Registers
The CSP uses 32 eight-bit external registers located in the main communication scanner components: IOC
bus connection, address compare, error reporting, and front-end scanner.
The external registers are connected to the CSP via the data in (odd) bus during read operations, and
data out (odd) bus during write operations. Their bits are set ON or OFF by the hardware or the micro-
code.
The external registers can be displayed or altered from the operator console, using the TSS functions.
Chapter 4. Transmission Subsystem (TSS)
4-15
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