The MIB ties all the components together. During microinstruction fetch, the
control chip generates an 11-bit address onto the MIB. Control store is accessed,
producing a 22-bit microinstruction, which is placed on the MIB. The low-order
16 bits go to the data chip, while the low-order 18 bits go to the control chip. The
high-order 4 bits control special processor board functions.
Figure 16.14 provides a still simplified but more detailed look at the LSI-11
control unit:The figure ignores individual chip boundaries.The address sequencing
scheme described in Section 16.2 is implemented in two modules. Overall sequence
control is provided by the microprogram sequence control module, which is capable
of incrementing the microinstruction address register and performing unconditional
branches. The other forms of address calculation are carried out by a separate
translation array. This is a combinatorial circuit that generates an address based on
the microinstruction, the machine instruction, the microinstruction program counter,
and an interrupt register.
The MIB ties all the components together. During microinstruction fetch, the
control chip generates an 11-bit address onto the MIB. Control store is accessed,
producing a 22-bit microinstruction, which is placed on the MIB. The low-order
16 bits go to the data chip, while the low-order 18 bits go to the control chip. The
high-order 4 bits control special processor board functions.
Figure 16.14 provides a still simplified but more detailed look at the LSI-11
control unit:The figure ignores individual chip boundaries.The address sequencing
scheme described in Section 16.2 is implemented in two modules. Overall sequence
control is provided by the microprogram sequence control module, which is capable
of incrementing the microinstruction address register and performing unconditional
branches. The other forms of address calculation are carried out by a separate
translation array. This is a combinatorial circuit that generates an address based on
the microinstruction, the machine instruction, the microinstruction program counter,
and an interrupt register.
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