Texas Instruments 990 Operation Manual page 171

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Parameter default values:
If the retries parameter is not specified, a value of
°
is used.
If duty is not specified, a value of 19
16
(25%) is used.
If the pgmable bits parameter is not specified, a value of I is used.
Description: This subcommand is used to define the physical characteristics needed to transfer
data to the PROM during the programming cycle. This subcommand may be used when a stan-
dard PROM data configuration is not desired or the PROM being used is not supported on the
Standard Control Information Cassette. The PROM characteristics are explained in detail in
paragraph 7.4.3.
The pulse width is entered as an integer number from 1 to 6. This number is then mapped into a
0.5 millisecond to 16.0 millisecond pulse according to the table of pulse widths in Appendix G.
This appendix also contains a table of the range of pulse widths allowed for the supported
PROMs.
The HIGH/LOW parameter specifies whether a PROM is to be programmed with Is or Os. For
example, the S287 PROM is initially all Is and must be programmed with Os. The programmable
bits parameter specifies the number of bits in the bit string to be physically transferred into the
PROM at a time. In most cases, with the exception of the erasable programmable read-only
memory (EPROM), only one bit should be programmed at a time. As the number of bits is
increased, the reliability of the programming process decreases.
When programming EPROMs, the entire bit string is programmed at once. For a description of
the EPROM programming process, see paragraph 7.6.2.
The retries parameter specifies the number of times to repeat the programming process if, after
programming the number of bits specified by the programmable bits parameter, a programming
failure occurs. The same bits will be reprogrammed until the correct data is transferred or the
retry count is depleted. When programming EPROMs, the retry parameter should always be
°
because of the special process involved in EPROM programming (paragraph 7.6.2).
The duty cycle determines the percentage of time that the programmable pulse (which causes the
actual transfer of data to the PROM) is on with respect to total cycle time (which includes a
delay time). Appendix G contains a table of the range of duty cycles allowed for the supported
PROMs.
Error messages:
PPOI Required parameter missing.
PP02 Parameter value outside permissible range.
Examples:
.PP,RC,4, 1,3,2, 10, 1
.PP,RC,8,0,4
7-21
Digital
Systems
Division