The J53 Formula
The PIC18F27J53 combines what the J-line split across branches: the 128 KB array of the PIC18F27J13 and the full-speed USB module of the J50 line, plus the J13 generation’s twelve-bit ADC. The 28-pin package carries 3.8 KB of SRAM, 48 MHz core, Deep Sleep at nine nanoamps, PPS, hardware RTCC, CTMU, three comparators, seven CCP plus three ECCP modules, two EUSARTs and two MSSPs – and no EEPROM, on a 2.0-3.6 V supply. USB instruments at the top of the 8-bit J-line live on this die.
Lock And Sweep
PIC18 configuration at 0x300000: CP0/CP1, WRT, boot-block bits. Erased config 0xFF; locked array 0x0000. Sweep:
– Array: 0x0000-0x1FFFF. – Configuration: 0x300000 window. – ID: 0x3FFFFE-0x3FFFFF.
Image Anatomy
The USB stack dominates: descriptor tables with ASCII product strings, endpoint handling, class logic, buffer descriptors in the dual-access RAM. Around it: the twelve-bit scan loops that mark J13 code, the RTCC wake scheduler, and emulated-EEPROM parameter blocks near the array top. The large CCP farm – ten time bases total – appears in the init section when the board drives multiple actuators. Verification focuses on descriptor integrity and the parameter block’s plausibility.
The Session
Identify, read the configuration window, sweep 0x0000-0x1FFFF, verify decoding. Nothing is erased; the part returns to service. Lock policy documented as found; clone parts can reproduce or omit it.
Deliverables
HEX file, annotated disassembly with the USB, analog, CCP and parameter regions labeled, configuration report, checksum tied to the die.
128 KB And A USB Port
The 27J53 combines the J13 core with a full-speed USB controller: 128 KB at 0x0000-0x1FFFF, 4 KB of SRAM, twelve-bit ADC, three comparators, three ECCP, two EUSART, two MSSP, RTCC, CTMU and PPS, in a 28-pin body. It is the largest non-graphics PIC18 in this form factor and it appears in instruments that log to a host over USB while running a real-time control loop.
Two Software Bodies In One Array
A USB-equipped 128 KB image splits cleanly: the stack and descriptor set live low, the real-time loop and its tables live high, and the boundary between them is where the main loop hands control back to the USB service routine. Reading that boundary out is what lets a client port the application to a new part without dragging the whole stack along, which is the usual reason a 27J53 is sent in.
– Array: 0x0000-0x1FFFF, 0x3FFF erased, 0x0000 protected. – Configuration: 0x300000-0x300007. – ID: 0x3FFFFE-0x3FFFFF.
Access Notes
Twenty-eight pins with USB, two serial ports and a twelve-bit converter leave the ICSP pads tight against the connector. Where the pads are inaccessible the part is lifted; where they are accessible the session still confirms continuity, because a shared PGC line with an external pull-up will hold the programmer in reset and the failure looks like protection.
What The Report Contains
A HEX file at word addresses, an annotated disassembly with the USB stack, the real-time loop and the coefficient tables separated by address range, a configuration report that records the protect and write-protect bits as found, and a checksum bound to the die. Nothing on the part is altered.
A Note On The 128 KB Boundary
The array ends at 0x1FFFF, and a programmer configured for a 64 KB device will silently stop at 0xFFFF and report success. That failure mode has produced more incomplete images than any other single cause, which is why the sweep length is stated explicitly in the report alongside the checksum.
Reporting The Address Range
Every report states the first and last address actually read, plus the count of non-blank words. Those three numbers make an incomplete session obvious at a glance, long after the fact.
To extract a locked 27J53, use the services desk or the contact form.