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CY7C63001C
CY7C63101C
Document #: 38-08026 Rev. *B
Page 5 of 28
6.1.3
Data Memory Organization
The USB Controller includes 128 bytes of data RAM. The
upper 16 bytes of the data memory are used as USB FIFOs
for Endpoint 0 and Endpoint 1. Each endpoint is associated
with an 8-byte FIFO.
The USB controller includes two pointers into data RAM, the
Program Stack Pointer (PSP) and the Data Stack Pointer
(DSP). The value of PSP after reset is 0x00. The PSP incre-
ments by 2 whenever a CALL instruction is executed and it
decrements by 2 whenever a RET instruction is used.
The DSP pre-decrements by 1 whenever a PUSH instruction
is executed and it increments by 1 after a POP instruction is
used. The default value of the DSP after reset is 0x00, which
would cause the first PUSH to write into USB FIFO space for
Endpoint 1. Therefore, the DSP should be mapped to a
location such as 0x70 before initiating any data stack opera-
tions. Refer to the Reset section for more information about
DSP remapping after reset. Figure 6-2 illustrates the Data
Memory Space.
after reset
Address
DSP
PSP
0x00
user
firmware
0x02
0x04
DSP
0x70
USB FIFO - Endpoint 0
0x77
0x78
USB FIFO - Endpoint 1
0x7F
Figure 6-2. Data Memory Space
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