Acorn Products Z80 SECOND PROCESSSOR 409 用户手册
5.10 The Tube
The Tube (IC1) is an Acorn custom IC which provides parallel
asynchronous communication between two processor systems, the BBC
Microcomputer (Host) and the Z80 second processor (Parasite). To each
processor system, it resembles a conventional peripheral device
comprising 4 read-only and 4 write-only, 8-bit registers. The Z80
accesses these registers via its I/O structure.
The Tube (IC1) is an Acorn custom IC which provides parallel
asynchronous communication between two processor systems, the BBC
Microcomputer (Host) and the Z80 second processor (Parasite). To each
processor system, it resembles a conventional peripheral device
comprising 4 read-only and 4 write-only, 8-bit registers. The Z80
accesses these registers via its I/O structure.
Fig. 5 Tube concept
5.10.1 Tube Registers
Each register has its own status byte, with a separate I/O address,
containing Register-Fu11 and Data-Available flags. The status byte for
Register 1 contains additional control bits that may be set by the
Host computer to enable interrupts or to reset the Z80. These control
bits may be read, but not set, by the second processor.
containing Register-Fu11 and Data-Available flags. The status byte for
Register 1 contains additional control bits that may be set by the
Host computer to enable interrupts or to reset the Z80. These control
bits may be read, but not set, by the second processor.
Fig. 6 shows the Tube registers in more detail