       ┌─────────────────────────────────────────────────────╖
       │ 4. FIELD PIU (priority interruptions unit).         ║
       ╘═════════════════════════════════════════════════════╝

 The  KM1804BH1  chip   is  8-bit  microprogramming   scheme  of   the
 vector  priority interruption  that can  be increased, which produces 
 priority processing of inquiry for interruptions from eight buses for 
 different  devices.  Fields  that  providing  management  work of PIU 
 is brought below:

 Includes:
           KM1804BH1 chip:
           BH1_MI² - Microinstruction;
           EINS    - Permit of the acceptance to instruction;
           EV      - Permit of the constant issue from ROM vectors
                     to DB (data bus).


 ┌─────────╖
 │ BH1_MI² ║  MICROINSTRUCTIONS OF THE KM1804BH1 CHIP.
 ╘═════════╝   ──────────────────────────────────────┘
 Purpose.
           The field of the KM1804BH1 chip  (priority interruption unit).
           The correspondence between opcode and executed function is
           provided in table. 
           ┌────┬─────────────┬─────────────────────────────────────┐
           │ MI │             │  microinstr. executed in BH1        │
           │3210│  Mnemonics  │     (with signal EINS = 0 )         │
           ├────┼─────────────┼─────────────────────────────────────┤
           │0000│ RESET;      │general clear                        │
           │0001│ RESET IR;   │clear IR                             │
           │0010│ CLR IR,Val; │clear IR signal from buses of mask   │
           │0011│ CLR IR,MR;  │clear IR with MR control             │
           │0100│ CLR IR,VR;  │clear IR with VR control             │
           │0101│ READ VR;    │read VR                              │
           │0110│ READ SR;    │read SR                              │
           │0111│ READ MR;    │read MR                              │
           │1000│             │installation of MR                   │     
           │1001│ LOAD SR,Val;│load SR                              │
           │1010│ CLR MR,Val; │bitwise clear MR                     │
           │1011│ SET MR,Val; │bitwise installation of MR           │
           │1100│ RESET MR;   │clear MR                             │
           │1101│ DI;         │prohib. of the request for interrup. │
           │1110│ LOAD MR,Val;│load MR                              │
           │1111│ EI;         │permit of the request for interrup.  │
           └────┴─────────────┴─────────────────────────────────────┘
 The note.
          Values  are  entered  in  binary  code, that indicated  by the  
          symbol '²'on the top of field identifier  (IM²). When entering
          the new command in this field is written code  of the  general 
          clear command, but signal  EINS=1  that's why  the instruction 
          is not executed. 


 ┌─────────╖
 │  EINS   ║  PERMIT THE INSTRUCTIONS ACCEPTANCE.
 ╘═════════╝   ─────────────────────────────────┘
 Purpose.
           The permit the instruction acceptance. Provides acceptance             ÉáºαÑΦÑ¡¿Ñ »α¿Ñ¼á ¿¡ßΓαπ¬μ¿¿. ÃíÑß»Ñ?¿óáÑΓ  »α¿Ñ¼  ¬
           to perform the instructions given in field BH1_IM².
 Level  :  0 - Active  (microinstruction on BH1 is executed)
           1 - Passive (microinstruction on BH1 is not executed).
 The note.
           Values  are  entered  in  binary  code.
           When entering the new command presenting the code of 
           the command on  KM1804BH1 chip is prohibited.

 ┌─────────╖
 │   EV    ║  PERMIT OF CONSTANT ISSUE FROM ROM VECTOR.
 ╘═════════╝   ────────────────────────────────────────┘
 Purpose.
           The active level of the signal provides the issue 16-bit 
           constant  from  8-address  vectors  ROM   on  system bus 
           data. The address for ROM is 3-bit vector, thet is issue 
           by PIC (priority  interruptions controller). 
           Values  of the constants,  prestored in ROM, are loading 
           when the system is adjusting.

Level  :   0 - Active  (constant output)
           1 - Passive (constant is not output because outputs of ROM 
                        are found in one third condition).
 The note.
           Values  are  entered  in  binary  code.
           When entering the new command issue of constants is prohibited.
