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HP 27130A
1/0 Address Space
The Z-80B CPU provides addressing capability for 256 distinct I/O port registers. The MUX
card uses only 47 I/O port register addresses: 16 are reserved for the four Z-80 SIOs, 12 are reserved
for the three Z- 80 CTCs, 12 are reserved for the MIC, and seven are reserved for the
BIe.
Table 3-3 shows the I/O addresses used by the card.
I
CAUTION
I
THE USE OF ANY OTHER ADDRESSES MAY CAUSE
IMPROPER OPERATION.
Z-808 Microprocessor CPU
The Z-80B CPU (U33) is an MOS LSI microprocessor which operates from a single +5-volt supply,
uses a single-phase clock, and has a typical instruction execution time of I microsecond. The data
bus is eight bits wide, and the address bus is 16 bits wide. All CPU pins are TTL compatible.
The Z-80B CPU employs a register-based architecture which includes two sets of six general-
purpose registers which can be used as individual 8-bit registers or 16-bit register pairs. Additional
8-bit registers include two sets of accumulator and flag registers, and the interrupt vector and
memory refresh registers. Additional 16-bit registers include the stack pointer, program counter,
and two index registers. The Z-80B CPU provides the intelligence for the MUX card to function
as a preprocessor for the I/O devices, thus relieving the host
computer
of
a considerable
amount of processing.
The functions of the Z- 80B CPU signals are shown in table 3-4.
Z
-80
S10/2 (Serial 1/0 Controller)
The MUX card uses four Z-80 S10/2 controller circuits (U43, U53, U63, and U73, see A42,
. 7
-1).
The
Z -
80 SI
0
/2 is a programmable serial
1/ 0
controller with two independent full-duplex
channels, each of which contains separate control and status lines. Each channel can be indepen-
dently programmed. On the MUX card, each of the eight channels is used as a fully programmable
asynchronous terminal controller.
Each SIO channel has two I/O addressable ports: one port for data transfer, and one for control in-
formation. Each control port has three read registers and eight write registers available for con-
trol information. The functions performed by the registers are shown in table 3-5.
Several of the SIO number 0 (U43) and SIO number I (U53) modem control output and modem
status input signals are. used for special functions, such as turning on the card's LED, sensing the
diagnostic test hood, etc. These special functions are described in table 3-6.
3-6
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