Power-On Reset; Summary Of Write Data Operation; Summary Of Read Data Operation; Cec Functional Theory - HP 7957A Hardware Manual

Hp disc drives hardware support manual
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Theory Of Opera tion
7957/7958
3-26.
POWER-ON RESET
The power-on reset circuit is activated by the +5V
output from Power Supply Assembly PCA-A3 and
produces Power Valid signal PV AL. At power on,
PV AL remains low for a t least 100 milliseconds
after the +5V output reaches 4.75V or higher.
Signal PV AL then goes to a high level. Signal
PV
AL
will also go low for at least 500 micro-
seconds prior to the +5V going below 4.75V.
Signal PV AL can be monitored at a test point on
the front of power supply PCA-A3 (see figure
4-4). PV AL is connected to CEC PCA-A2.
3-27.
SUMMARY OF WRITE DATA
OPERATION
Data is transferred from the host to the HP-IB
Interface IC over the HP-IB bus.
The data is transferred by DMA from the HP-IB
Interface IC to the buffers. This is referred to as a
remote DMA transfer.
The data is transferred by DMA from the buffer
to the DDC. This is referred to as a local DMA
transfer.
The data is serialized in the DDC and transferred
to the Disc Drive Assembly [HDA] PCA-AI. The
DDC generates the ECC (or Cycle Redundancy
Check [CRC]) bytes as it transfers the data to the
Disc Drive Assembly [HDA] PCA-A 1.
3-28.
SUMMARY OF READ DATA
OPERATION
Data is transferred from the Disc Drive Assembly
[HDA] PCA-Al to the DDC and deserialized in the
DDC. The DOC generates the ECC (or CRC) bytes
at the same time that the data is transferred into
the DDC.
The data is transferred by DMA from the DDC to
the buffers. This is referred to as a local DMA
transfer.
The data is transferred by DMA from the buffers
to the HP-IB Interface IC. This is referred to as a
remote DMA transfer.
3-12
The data is transferred from the HP-IB Interface
IC to the host over the HP-IB bus.
3-29.
CEC FUNCTIONAL THEORY
The CS80/ESDI Controller (CEC) PCA-A2 controls
the data transfer between the HP-IB host com-
puter implementing the CS/80 instruction set and
the Disc Drive Assembly [HDA] PCA-Al im-
plementing the ESDI interface standard.
Data
which is transferred between the HDA PCA-AI
and the host passes through the CEC where it is
buffered and changed to the correct format
required by its destination. The format of the data
which is transferred between the HDA and the
CEC is serial NRZ. Data transferred between the
host and CEC is over the HP-IB interface. The
CEC performs the following tasks.
• Receives high level disc control commands (such
as locate and read and locate and write) from
the host computer, and performs the low level
tasks necessary to execute these commands.
• Ensures that only error free data is passed back
to the host by performing retries and error
correction.
• Provides high level status reports to the host.
• Logs error and fault information.
• Performs self test at power on.
3-30.
BUS STRUCTURE
The CEC is made up of two buses, the micro-
processor bus and the DMA bus (see figure 3-6).
The DMA bus is used to transfer data between the
host and the HDA. These transfers are controlled
by DMA circuitry in the DDC. The data buffers
consist of 16 kbytes of static RAM divided into
two buffers (Buffer 0 and Buffer 1).
The DDC controls data transfers between the
HDA and the CEC. The HP-IB Interface IC con-
trols data transfers between the host and CEC.

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