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Section IV
FLIP-FLOP OR REGISTER
Abort Store (ABS) FF
Bit Counter
Direction (DI) FF
End-Of-Sector (EOS) FF
Read-Parity Error
(RPE) FF
RunFF
Sector Address
Coincidence FF
Sector Address Register
Sector Clock Phase
(SCP) FF
Sector Counter
Strobe (STR) FF
4-4
12606B
Table 4-3. Command Card Flip-Flops and Registers
FUNCTION
Cleared when an STC instruction addresses the data card. Set when the "not" RY or
"not" ACL signal becomes true, or when the disc is disconnected from the command
card. The state of the Abort Store FF can be determined by examining bit 3 of the disc
status word. (Refer to table 3-2.)
Counts "not" BC pulses received from the disc when writing or reading takes place.
Flip-flop BO contains the low-order bit. When 15 pulses have been received, the counter
contains a binary 1 in each position, and an associated "nand" gate indicates the
approach of the end of a word being transferred serially to or from the disc. The 16th
"not" BC pulse clears the counter, and the 17th attempts to advance the counter to 1.
However, the WRD FF is then in the reset condition, and the counter is held in the
cleared state. The counter thus contains zero at the start of the next word. The bit
counter is also cleared at the start of each sector by the second "not" SC pulse of the
sector. The bit counter runs only when disc writing or reading takes place.
Indicates whether disc writing or reading is taking place. Set for writing, reset for reading,
by an aT A/B instruction that addresses the command card.
Indicates when the end of a sector is reached on the disc. Set at the end of the 64th word
in the sector, and reset by the leading edge of the second "not" SC pulse of the next
sector.
Performs a meaningful function during disc reading only. Checks the state of
th~
RP FF
at the end of reading each word. If the RP FF found an odd number of logic O's in the
word (a parity error condition), the RPE FF is set. The RPE FF remains set, regardless of
additional parity errors, until an STC instruction addresses the data card. The state of the
RPE FF can be examined by checking bit 1 of the disc status word.
Set at the leading edge of the second "not" SC pulse for a sector in which disc reading or
writing will take place. Reset at the end of each sector.
Indicates that the sector specified for disc reading or writing has been reached. Set by the
first "not" SC pulse of the specified sector. Reset when disc operation is completed or
aborted.
Receives the address of the sector in which disc writing or reading will start. Flip-flop SO
contains the low-order bit. The register is loaded by bits 6 thru 0 of a word transferred
from the computer by an OTA/B instruction addressed to the command card. The
register retains its contents until a new sector address is loaded.
In the set condition between the trailing edges of each pair of "not" SC pulses. Serves as a
divide·by-two counter for the sector counter input, and is also used to differentiate
between the first and second "not" SC pulses.
Contains a binary number that is one greater than the address of the disc sector passing
the read/write heads. Flip-flop
seo
contains the low-order bit. The counter is advanced
by the second "not" SC pulse of each sector, and is cleared each time track origin passes
the read/write heads.
Set at the start of each word read or written. Reset at the end of each word read or
written. Controls the transfer of data from the data shift register to the output register
(when reading), or from the input register to the data shift register (when writing) on the
data card. Also controls setting of the WP FF on the data card (whtlD writing), and the
application of SRQ requests to the DMA system.
'
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