PITFALLS
- I/O features: an actual device may or may not have internal pull-ups (ca. 50-100kΩ) or bus-keeper (ATF devices only)
- Don‘t rely on device marking solely; check for presence/absence of I/O features by using the GALmate read function
- Clamping: pin voltages >7V may trigger erratic device behavior due to transition into Edit mode or Register Preload mode, i.e. pins are not clamped to VCC internally; use external diodes to VCC if clamping is desired
- Power Saving: use devices with power-down or zero-power mode feature with caution; verify your logic design on a regular device first; avoid slow signal transitions
- Expect erratic device behavior when applying slow signal transitions (rise time >100ns), especially as clock input signal; e.g. GAL oscillator circuits using two stage inverters
- A must read: ‘THE ODDITY’
- PALCE & PEEL devices: GALmate doesn‘t support PALCE (AMD) & PEEL (ICT) devices, though the generated design files are suitable for these devices
- National’s GAL22CV10 is equivalent to PEEL22CV10. That’s why GALmate won’t detect it.
- High Icc: the actual device operating current (1µA < Icc<130mA) depends on the device type, device mode and the programmed data
THE ODDITY
In 1985, Lattice introduced GAL as a versatile and reprogrammable alternative to the bipolar PAL. From 1989 on there were also revisions of the original GAL16V8/20V8, the GAL16V8A/20V8A, GAL16V8B/20V8B, etc.
Unlike the revisions, the original GAL16V8 & GAL20V8 provide no feedback into the AND Array when an I/O pin is configured as output in SIMPLE mode! (This also applies to GALs from licensees ST and National.) The OLMC’s Feedback Mux (FMUX) makes all the difference.
The crux of the matter: Most compilers assume existing feedback into the AND Array!
If your logic design requires output feedback from a certain pin then crosscheck with GALmate‘s Info function whether feedback is available. If you prefer to avoid any hassle then use ‘A’ or later revisions. GALmate detects ‘A’ or later revisions as GALxyV8A_Z and the original as GALxyV8.
Another option is to change to Complex or Registered mode. It is also (fail-) safe when using ATF devices.
Info: Original and revisions differ in device code and composition of the ACW. There is no difference in the JEDEC file. The GAL programmer software selects the suitable composition based on the device code.