RCA 301 Programmer's Reference Manual page 28

Card Feed Time
Card Feed Time is the time required to move a card from the select position until the first block is under the
read/write heads.
Card Return Time
Card Return time begins when the leading edge of the card passes under the read/write heads.
Card Reload Time
Card Reload Time is a nominal time required for the card to be reloaded into the designated magazine.
Drum Revolution Time
Drum Revolution Time is 60 ms., i.e., 40 ms. to pass the card and 20 ms. for gap time. Each block of 650
characters requires approximately 8 ms., and the inter-block gap is approximately 1 ms.
Block Select Timing
Under nominal operating conditions, it is possible to read or write to the next consecutive block as long as no
read/write head assembly movement is required and the Block Select and Read/Write commands are issued no more
than 100 ms. after the end of the preceding block. It is also possible to issue a no head movement Block Select within
the card gap time.
When a Block Select requires that the head be moved anywhere within positions 0 to 7 or anywhere within
positions 8 to 15, then 20 ms. is required to move the head positioner. When movement is made that crosses over
these boundaries, i.e., 7 to 8, 0 to 15, 8 to 7, etc., then 34 ms. is required to move the head positioner.
If a read or write is issued that misses the beginning of its specified block, the operation will be automatically
held off until the block approaches on the next revolution.
ACCURACY CONTROL
Address Verification and Card Absent Checking
To determine that the proper half-magazine has been selected, a bail sensor micro-switch is activated. This
identification of the selected half-magazine is compared with the requested address (Select instruction). To determine
that the proper card has been selected, a set of photocells are located on the track in position for reading the binary
coded selection notches on the top of the card. This reading is compared with the requested address (Select instruction)
before the card is placed on the capstan.
A head position sensor is mounted on the head assembly. A reading from the sensor is compared with the register
specifying the requested head position to insure proper head positioning. A constant check is made for proper head
positioning while reading or writing. A format notch is used to select the proper block.
An echo check is made while recording to assure that current is flowing through the selected head. Failure of
this check is considered an Address Verification error.
A check is made to ascertain that the returning card returns to the magazine that was originally selected.
Both Address Vertification and Card Absent error conditions will cause device inoperability.
When the Address Verification error occurs on a card that has been extracted, the device will go inoperable
immediately, and the card will be returned to its magazine after one revolution on the capstan. When the Address
Verification error occurs on a card that is being selected, the device will go inoperable at the time the card extract
would be attempted. The card will not be extracted.
When a Card Absent error occurs (First attempt) normal operation of the unit will be allowed until the
transport is cleared. Once all the cards are in their magazines, the hardware will make a second attempt to select the
card. If the Card Absent indication is received after this attempt, the unit will be made inoperable.
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