HP HP-97 User Manual

HP-97 Theory of Operation
DATA-————l ‘—
INS‘TRUCTION I DISPLAY l F\DDRESS l INSTRUCTION DISPLAY
Is 1
SYNC ——J———l J
TIME } f——— t t — —
Figure 2-5. Timing Diagram
2-15. In addition to being used to synchronize the system, SYNC is also
used to gate the 10-bit instruction that appears on IS at bit times tl46
through t55. During this time, SYNC distinguishes instructions from
addresses. Following an "IF" instruction on the IS bus, the subsequent
SYNC pulse is suppressed to allow a 10-bit address to be sent on the IS
bus.
2-16. At bit times t16 through t28, the IS line carries a 12-bit
instruction address from the ACT to the five ROMs, while display information
is carried from the ACT to the ROM during bit times tO through t7. At bit
times t0 through t3, a digit is carried from the ACT to the ROM's for
decoding and display. On the following word time, the next digit is sent
out. Sign, decimal point, and blanking information for the number is
carried to the ROM 0 during bit times t4 through t7.
2-17. PROGRAM AND DATA ROM
2-18. The ROM (read-only memory) consist of five ROMs each containing 1K
microprogrammed instructions that are used by the CPU to execute the
specified operations. Most operations require instructions stored in more
than one ROM. However, only one ROM is accessed at any time. When the
ROM address register in each ROM receives a 10-bit address on the ISA
line, the decoder in each ROM uses the four most significant bits of the
addresa to determine if the addressed location is in that ROM. The proper
ROM is enabled and transmits the addressed instruction on the ISA line;
the remaining ROMs are disabled. A timing circuit in each ROM synchronizes
the ROM's operation with the system timing using the ¢1, $2, and SYNC
2=5

HP HP-97 Specifications

General

Brand	HP
Model	HP-97
Category	Calculator
Language	English