2. Central Processing Unit (CPU)..............................2
2.1. Z80 Instruction Set with additions....................2
2.2. Registers.............................................2
2.3. Interrupt Modes.......................................3
- Like UARTs, with speeds from 150 baud to
38,400 baud
o 1-channel Clocked Serial I/O Port (CSI/O)
- For high-speed interprocessor communication
at 200K baud
o 2-channel Programmable Reload Timer (PRT)
- 16-bit counter driven by phi/20
o Dynamic RAM Refresh Circuit
- Refreshes dynamic RAMs without the need for
additional external support chips
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2. Central Processing Unit (CPU)
2.1. Z80 Instruction Set with additions:
o SLP (SLEEP Mode)
- Similar to HALT, but low-power
- Compare SLEEP and HALT
Function HALT SLEEP
Internal CPU Clock Active Stops
Int Crystal Oscill Active Active
Interrupt System Functional Functional
DRAM Refresh Active Stops
Internal I/O Sys Active Active
DMAC System Active Stops
Address Bus Active (Dummy) High
Data Bus Active (Dummy) Tristate
Exits
Reset Operational Operational
Interrupt Operational Operational
o MLT (Multiply)
- BC=B*C, DE=D*E, HL=H*L, SP=S*P
o Special I/O Instructions for On-Chip Devices
- IN0, OUT0 like IN, OUT
- OTIM, OTIMR, OTDM, OTDMR are Block I/O
Load from (HL) to port (C) for (B)
bytes, increment HL and C, decrement B
o Test Instructions (Non-Destructive AND)
- Test register, immediate, memory
- Test I/O port
2.2. Registers
o Same Set as Z80
o Interrupt Vector Register functions are
extended over the Z80
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� Central Processing Unit (CPU), Continued
2.3. Interrupt Modes
o 12 Interrupt Sources
- TRAP (Undefined Op-code Trap)
- NMI (Non-Maskable Interrupt from pin)
- INT0, INT1, INT2 (Maskable from pin)
- Internal Timers 0 and 1
- DMA Channels 0 and 1
- Clocked Serial I/O Port
- ASCI channels 0 and 1
o NMI is similar to NMI on the Z80
o INT0 is similar to Maskable Interrupts on Z80
- Mode 0 allows instruction fetch from
dat� bu� (1-byt� RST� lik� 8080)
- Mode 1 forces restart at 38H
- Mode 2 fetches low byte of vector table
from the address bus, high byte from I
register; this is address of address of
interrupt service routine
o INT1 and INT2 similar to INT0 Mode 2, but
low-order 5 bits are fixed (00000 for INT1
and 00010 for INT2), IL register provides
next 3 bits (set by user), and I register
provides upper 8 bits (set by user)
o Other interrupt sources, such as timers,
DMACs, CSI/O, and ASCI, function like INT1
and INT2; values supplied to low-order 5
bits are:
1. Interrupt is Signalled on NMI Pin
2. PC is pushed onto stack by CPU
3. Instruction at 66H is executed as first instruction of
Interrupt Service Routine
4. RETN instruction returns from Non-Maskable Interrupt
INT0, Mode 0
1. Interrupt is Signalled on INT0 Pin
2. Interrupting Device Places 1-byte Instruction (RST)
on Data Bus
3. Processor Performs Subroutine Call to Memory Locations
0, 8, 10H, 18H, 20H, 28H, 30H, or 38H
4. Interrupt Service Routine runs from there
INT0, Mode 1
1. Interrupt is Signalled on INT0 Pin
2. PC is pushed onto stack by CPU
3. Instruction at 38H is executed as first instruction of
Interrupt Service Routine
4. RETI instruction returns from Interrupt
INT0, Mode 2
1. Interrupt is Signalled on INT0 Pin
2. PC is pushed onto stack by CPU
3. Interrupting device places low-order 8 bits of address
of address table on data bus and is picked up by CPU
4. I Register contains high-order 8 bits of address of
address table
5. I Register + 8-bit Data Bus forms 16-bit Address of
address table entry low-byte; next byte is high-byte;
high-byte and low-byte combine to form address of
Interrupt Service Routine
6. PC is pushed onto stack by CPU
7. RETI instruction returns from Interrupt
8. Various devices work in this way, such as Z80-CTC,
Z80-DMA, Z80-SIO, Z80-DART, and they sense the RETI
instruction on the data bus to reset themselves as
well as providing the low-order 8 bits of the address
of the address table entry
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� Central Processing Unit (CPU), Continued
Interrupt Modes, Continued
o Short Explanations of Interrupts, Continued
-- Picture of INT0, Mode 2 Interrupt Vector Acquisition --
16-bit Vector Memory
-----------------------
| I Reg | Data Bus |
-----------------------
| | --------------------
Base Page Offset | High-order bits |
| | --------------------
-------------------------> | Low-order 8 bits |
| --------------------
... ...
| --------------------
-------------------------> | First entry, Low |
--------------------
INT1, INT2, and Internal Interrupts
1. Interrupt is Signalled on INT1 or INT2 Pin or by
Internal Interrupt Source (Timer 0 or 1,
DMAC 0 or 1, CSI/O, or ASCI 0 or 1)
2. Like INT0, Mode 2 Interrupts except:
Low-order 5 bits come from fixed code associated
with the source, next 3 bits come from IL register,
and high-order 8 bits come from I register
3. PC is pushed onto the stack
4. RETI returns from Interrupt
-- Picture of INT1, INT2, and Internal Interrupt Vector Acquisition --
16-bit Vector Memory
8 3 5
------------------------
| I Reg | IL | Code |
------------------------
| | --------------------
Base Page Offset | High-order bits |
| | --------------------
-------------------------> | Low-order 8 bits |
| --------------------
... ...
| --------------------
-------------------------> | First entry, Low |
--------------------
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� Central Processing Unit (CPU), Continued
Interrupt Modes, Continued
o Short Explanations of Interrupts, Continued
TRAP Interrupt
1. Triggered by undefined op-code fetch in 1st, or 2nd
byte of instruction
2. PC, which points to bad byte, is saved on stack
3. Vector to logical (depending on bank) address 0
4. Can be used to handle "extended" instruction set
ITC (Interrupt/Trap Control) Register
1. TRAP bit indicates if TRAP interrupt occurred; may
be reset by software
2. UFO (Undefined Fetch Object) bit indicates which opcode
TRAP occurred on
3. ITE0, ITE1, and ITE2 bits enable/disable INT0, INT1, and
INT2 interrupts
4. EI and DI instructions apply to enabled interrupts only
IL (Interrupt Low) Register
1. Used in conjunction with INT1 and INT2
2. High 3-bits may be read and written by software
I (Interrupt) Register
1. Used in conjunction with INT0 Mode 2, INT1, and INT2
2. Similar to Z80 I Register
3. May be read and written by software
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3. Memory Management Unit
o 19 address pins are coming off the chip (A0 to A18)
o the 19th pin is software selectable as address or
timer pulse (timer 1)
o all memory is divided into 64K banks, each bank containing
three areas:
---------------------
| |
| Common Area 1 |
| |
CBAR High ---> ---------------------
| |
| Bank Area |
| |
CBAR Low ----> ---------------------
| |
| Common Area 0 |
| |
---------------------
3.1. MMU Registers: CBAR, CBR, BBR
o CBAR (Common/Bank Area Register) contains the high-order
4 bits of the base address of Common Area 1 in
its high-order 4 bits (CBAR High) and the high-order
4 bits of the base address of Bank Area in its
low-order 4 bits (CBAR Low)
CBAR
4 bits 4 bits
-------------------------------------------
| Common Area 1 Base | Bank Area Base |
-------------------------------------------
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� Memory Management Unit, Continued
MMU Registers, Continued
o CBR (Common Base Register) specifies high-seven bits
of 19-bit effective address of Common Area 1; if
16-bit address is in Common Area 1 (high 4 bits
>= CBAR high), then add CBR to high 4 bits to
get high 7-bits of address
16 Bits Total
-------------------------------
Logical Address | High 4 | Lower 12 Bits |
-------------------------------
+ |
----------------- |
CBR | Hi 3 | Low 4 | |
----------------- |
|
|
| |
V V
19 Bits Total
--------------------------------------
Physical Address | High 7 Bits | Lower 12 Bits |
--------------------------------------
o BBR (Bank Base Register) specifies high-seven bits
of 19-bit effective address of Bank Area; if
16-bit address is in Bank Area (high 4 bits
>= CBAR low and < CBAR high), then add BBR to
high 4 bits to get high 7-bits of address
16 Bits Total
-------------------------------
Logical Address | High 4 | Lower 12 Bits |
-------------------------------
+ |
----------------- |
BBR | Hi 3 | Low 4 | |
----------------- |
| |
| |
V V
19 Bits Total
--------------------------------------
Physical Address | High 7 Bits | Lower 12 Bits |
--------------------------------------
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� Memory Management Unit, Continued
3.2. Address Translation Examples
1. CBAR Low = 0, CBAR High = F
Memory
----------------
| Common Area 1| 4K
F000H --> ----------------
| |
| Bank | 60K
| Area |
| |
0000H --> ----------------
Let CBR = 70H, BBR = 0
Memory Regions Mapped
Common Area 0: Not Mapped
Bank Area : 00000H to 0EFFFH
Common Area 1: 7F000H to 7FFFFH
o Source and Destination Memory Addresses are 19 bits
long (anywhere within 512K bytes)
o I/O addresses are 16 bits long
o Transfer Length is 64K bytes (16-bit length register)
o Channel 0 can do memory-to-memory, memory-to-I/O, and
memory-to-memory-mapped-I/O transfers; registers:
SAR0 Source Address Register
DAR0 Destination Address Register
BCR0 Byte Count Register
o Channel 1 can do memory-to-I/O transfers only; registers:
MAR1 Memory Address Register
IAR1 I/O Address Register
BCR1 Byte Count Register
o Other registers and some of their data:
DSTAT DMA Status
Enable/Disable Channels 0 and 1
Enable/Disable Interrupts 0 and 1
DMODE DMA Mode (Channel 0 Only)
Destination Memory or I/O
Source Memory or I/O
DCNTL DMA/WAIT Control
Memory Wait, I/O Wait
Memory-to-I/O or I/O-to-Memory
-- The DMA Concept--
1. Set up DMA Controller to Perform Transfer Function
Specify source, destination, etc
2. Initiate Transfer Function and then Proceed with
other Processing
3. Either check for transfer complete at later time or
be interrupted by DMA controller
4. With 2 DMA Channels, two DMA transfers can be going
on at once
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5. Asynchronous Serial Communication Interface (ASCI)
o Full Duplex
o 7- or 8-bit Data Length
o Software-controlled 9th Data Bit for Multiprocessor Comm
o 1 or 2 Stop Bits
o Odd, Even, or No Parity
o Parity, Overrun, or Framing Error Detection
o Programmable Baud Rate Generator to 38,400 baud
o Control Signals
Channel 0 has DCD (in), CTS (in), RTS (out)
Channel 1 has CTS (in)
o Can Generate Internal Interrupts
o Works with DMA Controllers
o Output can be in the form of interrupts or pulsing the
A18/TOUT pin
-- Operation --
1. Set Down Counter and Reload Registers
2. Set control flags (use interrupts, use TOUT, use both)
3. Start timer
4. When timer goes off, it starts over from reload
register value
5. Timer can be stopped at any time
