I came across this fairly concise list that provides detail and years behind each of the PPD revisions from Jandy. I thought the group might find this useful.

A Programmable Peripheral Device (PPD) with revision letter C to HH will operate with all PCBs with a 44 pin socket.
A Revision I or II PPD will only operate with a PCB which has a 44 pin socket and is a Revision I PCB.
A Revision J or newer PPD will only fit into a PCB with a 52 pin socket (second generation of PCB).
1994-Rev. A = Alpha testing.
1995-Rev. B = Beta testing.
1996-Rev. C = First production AquaLink RS.
1996-Rev. D = Allowed Cleaner JVA socket to be assigned to an auxiliary by turning on dip switch 7.
1996-Rev. E = Programmed ON times not recognized after freeze protection activates.
1996-Rev. F = RS 2/6 Sharing a heater support, light dimming on RS 4.
1997 Rev. G = First support for SpaLink RS, Cleaner JVA can be assigned without turning on dip 7.
1997 Rev. GG = Cancel button locks-up system.
1997 Rev. GGG = Correction to GG.
1998 Rev. H = First support f or LX / RS 485 connection, memory expansion to 128K of ROM, SpaLink reads pool temperature and OFF when the system is not on.
1998 Rev. HH = Corrects time calibration problem with Rev. H.
1998 Rev. HH 232 = Support for RS 232 Serial Adapter.
2000 Rev. I = First support for OneTouch, includes serial adapter support. Note Rev I will only operate in a Rev. I PCB.
2000 Rev. II = Corrects problem with auxiliaries assigned to f reeze on OneTouch.
2002 Rev. J = Change to 52 PIN PPD and new socket on AquaLink RS PCB.
2002 Rev. JJ = Corrects problem with auxiliaries assigned to freeze on OneTouch.
2003 Rev. K = Support for FlowLink, items manually turned on will reactivate after going to Auto/Service/Time Out.
2004 Rev. L = Color Light Control, PC Docking, Laminar Light Pulse Control (LPC4), Chiller/Heat Pump operation, Run Time (circuits can be set to run manually f or 1 to 10 minutes or for 10 minutes to 2 hours in 10 minute increments). Will communicate directly with AquaPure Chlorine Generator only.
2006 Rev. M = Support for AquaPalm wireless remote, Change chlorine production from AquaPure. AquaPure (revision must be 11230A05 or newer). Assign OneTouch buttons to SpaLink RS buttons.
2006 Rev. MM = Corrects problem when entering into lights labels.
2006 Rev. MMM = Corrects problem associated with daylight savings which caused the AquaPalm to jump lines. Light dimming can be adjusted from AquaPalm.


2007 Rev. N = Complete change to PCB. The operating chip is no longer a PPD, it is now a CPU (Central Processing Unit) board. The AquaLink RS can be connected via the RS 485 line to a Jandy AE Heat Pump &/or a Jandy LXi Gas Heater.
2008 Rev O = Communication with Variable Speed pumps.
2009 Rev P = Communication with ChemLink, LM3, AutoClear Plus & DuoClear.
2010 - Rev Q = first support for Touch Screen panel.
2012- Rev R = internet control of Jandy Aqualink system via smartphone or web