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MCS7840
USB-2.0 to Four Serial Ports
Page 10
Rev.
1.2
Transmitter Holding Register & Receiver Holding Register (THR & RHR):
Data is written into the bottom of the THR queue & read from the top of the RHR queue completely
asynchronously to the operation of the transmitter & receiver. The size of the FIFOs is dependent upon the
setting of the FCR register.
Data written to the THR when it is full, is lost. Data read from the RHR when it is empty, is invalid. The empty
and full status of the FIFOs is indicated in the Line Status Register.
Register:
THR
Description:
Data to be transmitted
Offset:
0
Permissions:
Write Only
Access Condition:
LCR[7] = 0
Default Value:
(unknown) – based on memory
Bit[7]
Bit[6]
Bit[5]
Bit[4]
Bit[3]
Bit[2]
Bit[1]
Bit[0]
Data to be transmitted
Register:
RHR
Description:
Data to be received
Offset:
0
Permissions:
Read Only
Access Condition:
LCR[7] = 0
Default Value:
(unknown) – based on memory
Bit[7]
Bit[6]
Bit[5]
Bit[4]
Bit[3]
Bit[2]
Bit[1]
Bit[0]
Data to be received
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