The Spectrum Next's z80 processor can only directly address 64k of memory but the ZX Spectrum 128 and ZX Spectrun Next models are equipped with far more physical memory than this.
Bank switching is used to access this extra memory.
This example explains how to implement bank switching in C code using z88DK compiler.
Demo of how to use the z88dk adt p_forward_list
Hello World C program for the ZX Spectrum Next using the z88dk compiler.
Z88DK is a collection of software development tools that targets the 8080 and z80 family of machines. It allows development of programs in C, assembly language or any mixture of the two. What makes z88dk unique is its ease of use, built-in support for many z80 machines, including ZX Spectrum Next, and its extensive set of assembly language library subroutines implementing the C standard and extensions.
The Z88DK offers several C Run Times (CRT) that can be selected using -startup at compile time. These CRTs provide the initialisation code that is called before main(). Some of them provide a simple tty device which supports controls codes such as \x16nn move cursor to X,Y.
NB when installing z88dk on Windows you need to set up the environment variables
The following program prints "Hello World" near the middle of the screen and then loops forever changing the border between red and yellow.
The resultant .nex file can be loaded by a ZX Spectrum emulator such as
CSpect or copied over and run on real ZX Spectrum Next hardware.
An overview of how to connect a LoLin NodeMCU v3 IoT device to the Azure IoT Hub using the Arduino IDE.
The Azure IoT Hub provides a cloud-hosted solution back-end to connect backend applications with IoT devices.
The LoLin NodeMCU v3 device is a wireless IoT device based on the ESP8266 microchip. For more info see First Impressions of the LoLin MCUv3
The high-level steps to connect the LoLin NodeMCU IoT to the Azure IoT cloud are
For steps 1 to 3 refer to the following guide for step by step instructions to setup an Azure IoT Hub, register a LoLin device, setup the Arduino libraries and run your first IoT program
Microsoft publish a C SDK that supports a wide range of IoT devices including the LoLin NodeMCU. Developers can use this C SDK to develop programs to connect devices to the Azure IoT Hub.
The LoLin NodeMCU is based on the ESP8266 Microcontroller (MCU) and is what Microsoft call a constrained device in that it has comparatively limited resources, such as memory, compared to devices based on a CPU.
The Azure IoT C SDK includes a version that is optimised to run on constrained devices. For example, it is single threaded whereas some of the functions in the unconstrained version will spin up seperate threads to complete jobs in the background.
These C libraries need to be installed in the Arduino IDE environment
using its Library Manager as explained in the guide above. Once installed we can include these libraries in our programs with
#include <AzureIoTHub.h>
Microsoft publish a detailed developer how-to guide for the Azure IoT device SDK which explains how to use the API with examples. Find it here Dev guide for the Azure IoT device SDK for C
Microsoft provide a sample program 'iothub_ll_telemetry_sample' to demonstrate use of the Azure IoT SDK on the ESP8266.
The key functions called by the demo program are
How to setup the Roland TR-8 with Ableton Live
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| Live's MIDI preferences |
Now when you play a MIDI note on the MIDI track configured in step 3 (play C1 for a kick) you should hear the TR-8 audio on the audio track configured in step 4.
The 4bit Juno ALU is based around an 74 series 181 ALU arithmetic logic chip which implements mathematical and logical operations. The '181 was used in many early minicomputers like the NOVA and PDP-11.
The mathematical operations include addition, subtration with or without carry and the logical operations include logical ∧ AND, NAND, ∨ OR, NOR, ⊕ XOR and shift.
The inputs to the ALU are the DR register and the data bus. Operations are performed by loading the DR register with the first operand and then placing the second operand on the data bus. The output of the operation is stored in A register.
The Carry input is selected using the carry multiplexer and can be (0) zero, (1) one or (2) the carry bit of the status register.
The Carry and Comparator result of the operation can be saved to the status register using LD_Carry and LD_Comparator.
Each CPU instruction such as "LDA <address>" is implemented as a sequence of micro code operations.
Each micro code operation sets the CPU control signals high or low and holds them for a clock cycle before moving to the next micro code operation in the sequnce.
These CPU control signals are encoded as data in ROM chips. A '1' sets the control signal high and '0' sets the control signal low.
The ROM contents are addressed using an 8-bit address, 4 bits for the instruction being executed plus 4 bits for the step in the micro code sequence. Therefore, the Juno PC supports 16 CPU instructions and each instruction can be up to 16 steps in length.
To support the number of control signals needed several 8-bit ROM chips are used.
The current instuction being executed is held in the 4-bit Instruction Register (IR). Each instuction has a unique number between 0 and 15.For example, the NOP instuction is instuction 0.
At the start of every instruction the Program Counter (PC) register must hold the address of the instruction to be executed and the first step of the micro code sequence is to load the IR with the instruction pointed to by PC.
The micro code controller will then step through the sequence of operations for the instruction.
NB on starting a new instruction IR will actually hold the previous instruction and execute step 0 which will load IR with the instruction at address PC.
The micro code step sequencer is implemented using a 4-bit counter. To start a new instruction the counter is reset to zero by the previous instruction. The counter is then incremented by the clock until it is reaches the last step in the sequence. The last step in sequence must reset the counter to zero using the uCounterRest control signal to start the next intruction.
The counter is implemented using a 74HC393 counter which features a clock input that increments the counter on a falling edge. A clock cycle is therefore from one falling edge to the next and the control signals are held for the duration of this clock cycle.
The CPU control signals for load, or write, operations are logically AND with the clock signal so that control signal goes positive half way through the clock cycle. For example, registers are implemented using postive edge triggered chips such as the 74HC574.
This control sequence ensures there is time for the control signals and digital circuits to stabalise before performing the load / write actions.
A clock signal is a periodic signal that switches between high and low and is used to coordinate the actions of digital circuits.
A clock cycle is the time between two rising edges and consists of
Sequential digital circuits can be designed to be
In this way the operation of a CPU can be contolled and co-ordinated. For example, to load a register with the contents from a memory address location the clock can co-ordinate the operation as follows:
To achieve this timing the CPU control signals for load, or write, operations are logically AND with the clock signal so that control signal goes positive half way through the clock cycle. For example, registers are implemented using postive edge triggered chips such as the 74HC574.
