UM10360 All information provided in this document is subject to legal disclaimers. © NXP B.V. 2013. All rights reserved.
User manual Rev. 3 — 19 December 2013 251 of 841
NXP Semiconductors
UM10360
Chapter 11: LPC176x/5x USB device controller
11.12.11 Select Endpoint/Clear Interrupt (Command: 0x40 - 0x5F, Data: read 1
byte)
Commands 0x40 to 0x5F are identical to their Select Endpoint equivalents, with the
following differences:
• They clear the bit corresponding to the endpoint in the USBEpIntSt register.
• In case of a control OUT endpoint, they clear the STP and PO bits in the
corresponding Select Endpoint Register.
• Reading one byte is obligatory.
Table 248. Select Endpoint command bit description
Bit Symbol Value Description Reset value
0 FE Full/Empty. This bit indicates the full or empty status of the endpoint buffer(s).
For IN endpoints, the FE bit gives the ANDed result of the B_1_FULL and
B_2_FULL bits. For OUT endpoints, the FE bit gives ORed result of the
B_1_FULL and B_2_FULL bits. For single buffered endpoints, this bit simply
reflects the status of B_1_FULL.
0
0 For an IN endpoint, at least one write endpoint buffer is empty.
1 For an OUT endpoint, at least one endpoint read buffer is full.
1 ST Stalled endpoint indicator. 0
0 The selected endpoint is not stalled.
1 The selected endpoint is stalled.
2 STP SETUP bit: the value of this bit is updated after each successfully received
packet (i.e. an ACKed package on that particular physical endpoint).
0
0 The STP bit is cleared by doing a Select Endpoint/Clear Interrupt on this
endpoint.
1 The last received packet for the selected endpoint was a SETUP packet.
3 PO Packet over-written bit. 0
0 The PO bit is cleared by the ‘Select Endpoint/Clear Interrupt’ command.
1 The previously received packet was over-written by a SETUP packet.
4 EPN EP NAKed bit indicates sending of a NAK. If the host sends an OUT packet to a
filled OUT buffer, the device returns NAK. If the host sends an IN token packet
to an empty IN buffer, the device returns NAK.
0
0 The EPN bit is reset after the device has sent an ACK after an OUT packet or
when the device has seen an ACK after sending an IN packet.
1 The EPN bit is set when a NAK is sent and the interrupt on NAK feature is
enabled.
5 B_1_FULL The buffer 1 status. 0
0 Buffer 1 is empty.
1 Buffer 1 is full.
6 B_2_FULL The buffer 2 status. 0
0 Buffer 2 is empty.
1 Buffer 2 is full.
7 - - Reserved, user software should not write ones to reserved bits. The value read
from a reserved bit is not defined.
NA
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