I/O modules

AXO-003 — Shift-register lab PMOD module

Catalog #3 in the AruviX output line, level L2 (serial shift — roll your own SPI). Two cascaded 74HC595 shift registers: the first drives a single-digit 7-segment display, the second drives 8 discrete LEDs. The QH' → SER cascade is the lesson: after bit-banging this chain the student has independently invented SPI daisy-chaining.

Circuit review & bench-test guide →

Components#

Every placed component, with the reason it is on the board. Extracted directly from the schematic, so this cannot drift from the design.

Signals#

Net labels used in the schematic, which are also the names the HDL top level should use.

3V3 CASCADE GND LED1 LED1_A LED2 LED2_A LED3 LED3_A LED4 LED4_A LED5 LED5_A LED6 LED6_A LED7 LED7_A LED8 LED8_A RCLK SEG_A SEG_A_S SEG_B SEG_B_S SEG_C SEG_C_S SEG_D SEG_DP SEG_DP_S SEG_D_S SEG_E SEG_E_S SEG_F SEG_F_S SEG_G SEG_G_S SER SRCLK SRCLR_N

Production status#

Source: boards/io-modules/axo-003-shift-lab

Catalog #3 in the AruviX output line (../README.md), level L2 (serial shift — roll your own SPI). Two cascaded 74HC595 shift registers: the first drives a single-digit 7-segment display, the second drives 8 discrete LEDs. The QH' → SER cascade is the lesson: after bit-banging this chain the student has independently invented SPI daisy-chaining.

Status: schematic generated, ERC clean (0/0), netlist reviewed. PCB layout not started. Not released.

What it teaches#

• What SPI is: shift on clock edge (SRCLK), latch on a separate strobe (RCLK), chain devices through the overflow output (QH').
• Bit order made visible: shift 16 bits MSB-first, the first 8 crawl through U1 into U2's LEDs, the last 8 stay in U1's 7-seg digit.
• Hex-to-segment decode (the seg7 decoder from axo-002, minus the scan).

Design#

• 2× 74HC595D,118 (SOIC-16, Nexperia), both ~OE hard-wired low, shared SRCLK/RCLK, shared ~SRCLR with a 10 kΩ pull-up (chain runs even if the host leaves PMOD pin 4 unconfigured; drive low to blank).
• U1 QA..QG → segments A..G, QH → DP, through 220 Ω each (~6 mA/segment at 3.3 V). Display is a Kingbright KCSC02-105 — stock single-digit 0.2" common-cathode symbol and footprint verified (Display_7Segment: KCSC02-105), so no discrete-LED fallback was needed. Both CC pins to GND.
• U2 QA..QH → LED1..LED8, green 0603 (APT1608SGC) + 330 Ω each (~4 mA).
• Everything active-HIGH (common cathode / grounded LED cathodes).
• 100 nF per 74HC595.

Regenerate#

python3 generate_design.py

Remaining for release#

• [ ] PCB layout (20 × 25 mm outline), DRC, fab outputs
• [ ] hdl/: bit-bang shift driver + seg7 decode reuse, testbench, ECP5 demo
• [ ] BOM export and availability check, design-review checklist