Firmware revisions through 1.620 use RPI
Firmware revisions from 1.628 use RPI+
Check the response to "ATI3" for firmware info.
RPI FAQ
Note: Some older ACF modems can operate in either RPI+ or the traditional hardware ECC mode.
RC144ATFD-x US/Canada
RC144ATF-x US/Canada
RCV144ATF-x US/Canada
RC144ATFWD-x + 128k-byte External ROM Multicountry
RC144ATFW-x + 128k-byte External ROM Multicountry
RCV144ATFW-x + 128k-byte External ROM Multicountry
RC144ATFWD-x + 8k-byte External ROM Single country
RC144ATFW-x + 8k-byte External ROM Single country
RCV144ATFW-x + 8k-byte External ROM Single country
Notes:
Model options:
x Host/DTE interface (P = Parallel host; S = Serial DTE)
D Data only (no fax).
V Voice (including business audio for parallel interface)
W World class support.