It's this one: XC95144XL
That has this in the data sheet (Darn . . .
Design Security: XC9500XL devices incorporate advanced data security features which fully protect the programming data against unauthorized reading or inadvertent device erasure/reprogramming. Table 3 shows the four different security settings available. The read security bits can be set by the user to prevent the internal programming pattern from being read or copied. When set, they also inhibit further program operations but allow device erase. Erasing the entire device is the only way to reset the read security bit. The write security bits provide added protection against accidental device erasure or reprogramming when the JTAG pins are subject to noise, such as during system power-up. Once set, the write-protection may be deactivated when the device needs to be reprogrammed with a valid pattern with a specific sequence of JTAG instructions.
I'll contact Dave Prosser today and see what he says.
Parts: UM6502CE, GAL22V10D, GAL16V8D, AS6C62256A, TC514400AZ, WD1772, R6522, TMS27C512, AT28C256
Products: ARA II, ARA III, ABR, ATI, AP6, MGC, AP5 . . .
For a price list, contact me at: Retro Hardware AT dave ej hitchins DOT plus DOT com