NEC switch - Manual (Page 98)

CHAPTER 8 USB FUNCTION
User’s Manual U12978EJ3V0UD
98
8.2 USB Function Features
The features of the on-chip USB function provided for the µPD789800 Subseries are described below.
(1) Video display devices and human interface devices are assumed to be the target applications. For this
reason, only Endpoint 0 for control transfer and Endpoint 1 for interrupt transfer are supported.
(2) 1.5 Mbps (low speed) data transfer using a 6.0 MHz system clock is supported.
(3) The following buffers are provided on-chip.
• Receive token bank: 1 bank (3 bytes)
• Receive data bank: 1 bank (9 bytes)
• Transmit data bank: 2 banks (9 bytes × 2)
(4) NRZI (Non Return to Zero Invert) decode/encode function specified by the USB communication protocol, bit
stuffing function, and on-chip CRC (Cyclic Redundancy Check) function are also provided and automatically
executed.
8.3 USB Function Configuration
The USB function consists of the following hardware.
Table 8-1. Configuration of USB Function
Item Configuration
Buffer Receive bank switching ID detection buffer (internal buffer)
Registers Transmit/receive pointer (USBPOW)
Receive token PID (USBRTP)
Receive token address L, H (USBRAL, USBRAH)
Receive data PID (USBRD)
Receive data address (USBR0 to USBR7)
Transmit data PID bank 0 (USBTD0)
Transmit data bank 0 address (USBT00 to USBT07)
Transmit data PID bank 1 (USBTD1)
Transmit data bank 1 address (USBT10 to USBT17)
Data/handshake packet receive byte number counter (DRXCON)
Data packet transmit byte number counter 0, 1 (DTXCO0, DTXCO1)
Token PID compare register (TIDCMP)
Token address compare register (ADRCMP)
Data/handshake PID compare register (DIDCMP)
Control registers USB receiver enable register (USBMOD)
Data/handshake packet receive mode register (URXMOD)
Packet receive status register (RXSTAT)
Data/handshake packet receive result store register (DRXRSL)
Token packet receive result store register (TRXRSL)
Data packet transmit reservation register (DTXRSV)
Handshake packet transmit reservation register (HTXRSV)
USB timer start reservation control register (USBTCL)
Remote wakeup control register (REMWUP)
Receive token bank
Receive data bank
Transmit data bank 0
Transmit data bank 1