ACS ACR122U is an USB NFC reader, PC/SC and CCID compilant, based
on NXP PN532 chip.
Internally, it's build of MCU, PN532 and an antenna. MCU makes the
device CCID and PC/SC compilant and provide USB connection.
In this achitecture, a host cannot talk directly to PN532 and must
rely on MCU. Luckily, MCU exposes pseud-APDU through PC/SC Escape
mechanism which let the host to transmit standard PN532 commands
directly to PN532 chip with some limitations.