5 Theory of Operation
130 Keysight 34970A/34972A Service Guide
The custom ASIC, U209, provides:
– Memory Address mapping – The main controller multiplexes address and data
on the same bus. U209 latches the address and drives a separate memory
address bus (MA(19:1)). U209 allows the main controller to access a much
larger memory space than its 16-bit address bus would allow. It also partitions
memory into separate data and instruction segments and a “mappable”
segment that can be used for either data or instructions.
– Communications – U209 provides three serial communication ports. A 187.5
kbit/second, 9 data bit, UART for communicating with the isolated backplane
(FLT_BPDO and FLT_BPDI_N). A duplicate, 9-bit UART to communicate with
the front panel (FPDO and FPDI). And a simple, 1.5 Mbit/second, clocked
shift-register to control the configuration registers on the DMM assembly
(CFG_SCK, CFG_DO, and CFG_DI).
– Real Time Clock – U209 provides time of day and date, a periodic interrupt,
and a squarewave generator. The date is based on a 100 year calendar (it
accurately tracks leap years until its two digit year counter rolls over). U209
uses the battery-backed +5V_NV supply.
– DMM support – U209 provides conversion logic for the analog-to-digital
converter and a counter for both the ADC and the frequency measurement
features of the DMM. When used for the ADC, the COMP input functions both
as a clocked comparator and the slope counter input. When used for
frequency measurement, FREQIN is the input to the counter. In both cases, the
8-bit counter produces the lower bits of a 24-bit counter. The counter overflow
signal, CNT, is counted by U205 to produce the upper 16-bits of the count. The
SYNC signal produced by U205, is used to latch the count.
Device U201 is a 512 byte, ferroelectric RAM that is accessed via a serial
interface. This device only contains data relevant to the A1 assembly. This data is
combined with data retrieved from A4U450 to completely calibrate the internal
DMM. The two devices, although on different assemblies, share the same I/O
signals, CALSCK and CALDAT, that allow them to be read (and written) by U205.
To Next Page
Loading...
Need help?
General
