Assembly Loader and RAM Write Path
A clocked assembly program loader writes an eight-byte compiled image into 256 × 8 RAM through address, data, WE, and CS connections. RAM outputs are unconnected, so the circuit demonstrates loading rather than a visible read path.
What You'll Learn
- Trace an 8-bit address bus and an 8-bit data bus from a loader into RAM.
- Explain how CS, WE, and a rising clock edge coordinate a memory write.
- Interpret a 256 × 8 organization as 256 byte-wide locations.
- Verify the persisted eight-byte image in RAM without inventing an unwired read output.
- Distinguish loading machine bytes from executing them in a processor.
How It Works
This production canvas is a clocked program-loading path, not a manually operated RAM read/write panel. It contains one ASSEMBLY_PROGRAM_LOADER, one 256-word × 8-bit RAM, one 1 Hz clock, and one Enable switch.
The loader's outputs A0–A7 connect to the RAM address inputs, D0–D7 connect to the RAM data inputs, WE connects to RAM WE, and CS connects to RAM CS. The same clock drives both components. One switch fans out to the loader's EN, A_OE, and D_OE inputs, so enabling the loader also permits it to drive both buses. During an active load, each eligible rising edge presents one compiled byte at the corresponding address and asserts the controls required for the RAM write.
The persisted compiled image contains eight bytes beginning at address 0: 10 4F 21 75 61 60 60 60 in hexadecimal. This lesson treats that byte sequence as the payload and focuses on the transfer mechanism rather than assigning runtime semantics to the program.
The RAM's eight data outputs are unconnected, and no output-enable source, lamp, or display is present. Consequently, the visible lesson is the write path; stored contents must be examined with the component inspector.
Try It Step-by-Step
Set the listed controls in the embedded circuit, then compare the observed modeled state with the expected result.
- 1Loader action=Inspect compiled imageExpected:
Compiled bytes = 10 4F 21 75 61 60 60 60 (hex)What you'll see:Open the loader inspector and verify the authoritative eight-byte compiled image before reasoning about the transfer. - 2Clock=first rising edgeEnable=1Loader action=Compile, then Load into RAMExpected:
After the first enabled rising edge, RAM[0x00] = 0x10What you'll see:After compiling and choosing the loader's RAM-load action, the first enabled rising edge writes byte 0x10 to address 0x00. - 3Clock=eight rising edges from restartEnable=1Expected:
RAM[0x00..0x07] = 10 4F 21 75 61 60 60 60 (hex)What you'll see:Eight enabled rising edges transfer the complete image to consecutive addresses 0x00 through 0x07; inspect the RAM to confirm it. - 4Clock=additional rising edgeEnable=0Expected:
With Enable = 0, an additional edge does not advance or write the loaderWhat you'll see:Taking Enable low disables the loader and releases its address and data buses, so further clock edges cannot advance an active transfer.
Components Used
Applications and Design Context
Boot and programming paths. Processors, microcontrollers, and FPGAs need controlled mechanisms that place code or configuration data into executable storage before normal operation.
Memory initialization in simulation. Testbenches and educational tools preload deterministic byte images so later datapath behavior starts from a known state.
FPGA block RAM initialization. Toolchains convert source artifacts into memory images that initialize or populate on-chip RAM resources.
In-circuit programming. Debuggers and bootloaders transfer address/data records into target memory while coordinating write strobes and device selection.
Bus-interface education. The separate address, data, control, and clock paths provide a compact example of a synchronous memory write interface.
Frequently Asked Questions
Which signals connect the loader to RAM?
The loader presents an 8-bit address and an 8-bit data word. Its WE and CS outputs connect to the corresponding RAM control pins, and the shared clock supplies the write edge. This canvas does not use manual address or data switches.
Why is this RAM described as 256 × 8?
The address bus has eight lines, A0 through A7, so it selects 2^8 = 256 locations. The data bus has eight lines, D0 through D7, so each location stores one byte.
What does the Enable switch control?
A single switch drives the loader's EN, A_OE, and D_OE inputs together. When it is low, the loader is disabled and releases its address and data outputs; when it is high, an active load can advance on rising clock edges.
Where is the RAM read-data output shown?
No output indicator is wired to the RAM's data pins, and the RAM output-enable input is not driven on this canvas. Verify memory through the RAM inspector rather than expecting a lamp or display to show a read value.
Does this circuit execute the loaded program?
No. The circuit demonstrates compilation-to-memory transfer only. A processor would additionally need a program counter, instruction register, decoder or control unit, registers, an ALU, and a coordinated datapath to execute the stored bytes.