The FAQ states the CPU is an ARM1176JZF-S which is an ARM11 Classic processor the processor details are available here on the ARM website.
The Technical Reference Manual is available via the ARM documentation centre
Select: ARM11 Processors -> ARM1176 -> RM1176JZF-S Technical Reference Manual
(Or as a PDF from here)
The ARM Architecture Reference Manual that covers the ARM11 instruction set is the
"ARM Architecture Reference Manual ARMv7-A and ARMv7-R edition":
This manual describes the instruction set, memory model, and programmers' model for ARMv7 (A&R profile) compliant processors, including:
It also describes the later ARMv6 architecture releases for ARM11 processors, and describes Thumb-2 and the TrustZone security extensions.
It can be downloaded from the ARM website here (registration is required).