NEC Network Controller uPD98502 - Manual (Page 337)

CHAPTER 6 USB CONTROLLER
Preliminary User’s Manual S15543EJ1V0UM 337
6.5.3 Data transmit modes
USB Controller supports two transmit modes. These modes differ only in whether a zero-length USB packet is
transmitted after the last USB packet of a data segment. In all other aspects, they are identical. The transmit mode is
switched using the TM bit (Bit 19) of the USB EP1 EndPoint Control Register (Address: 1000_1024H) and USB EP3
EndPoint Control Register (Address: 1000_102CH).
Cautions 1. The setting of the TM bit applies only to EndPoint1 and EndPoint3.
2. When EndPoint0 and EndPoint5 are used to transmit data, only NZLP mode is used.
(1) SZLP (Transmit Zero Length Packet) mode
In this mode, when the last USB packet size of a data segment is equal to the value in the MAXP field, a zero-
length packet is transmitted after the completion of data segment transmitting.
When the last packet size is less than the value in the MAXP field, the last Short Packet is transmitted and any
zero-length packet is not transmitted.
(2) NZLP (Non Zero Length Packet) mode
In this mode, even when the last USB packet size of a data segment is equal to the value in the MAXP field, any
zero-length packet is not transmitted after the last packet transmission.