Editing Sinclair QL (section)

== Architecture ==

[[File:Sinclair QL block diagram.png|center|thumb|700px|Sinclair QL system block diagram (Figure 1.3 of the QL Service Manual): the 68008 processor with the ZX8301 master chip, ZX8302 peripheral chip and 8049 IPC.]]

The machine is built from the 68008 plus three support devices:<ref name="wp" /><ref name="sm">''[[Sinclair QL Service Manual]]'', Sinclair Research Ltd. Section 1 (System Description), Section 4 (Fault Diagnosis and Repair) and Section 5 (Parts Lists).</ref>

{| class="wikitable styled-table" style="width:95%; text-align:left;"
|+'''Sinclair QL main devices'''
! Device !! Position !! Function
|-
| Motorola 68008 || IC18 || CPU at 7.5 MHz; 32-bit internal registers, 8-bit external data bus
|-
| ZX8301 "Master Chip" || IC22 || Video display generator and DRAM refresh; made by Plessey (CLA2310, later CLA2345)
|-
| ZX8302 "Peripheral Chip" || IC23 || Microdrives, RS-232 transmit, QLAN network, real-time clock, link to the IPC; made by NCR
|-
| Intel 8049 IPC || IC24 || Keyboard and joystick scanning, RS-232 receive and sound; licensed 8049 with custom Sinclair firmware, made by Philips or NEC
|-
| HAL || IC38 || Address decode; added at Issue 6, replacing IC17 and IC27
|}

The ZX8301 divides the 15 MHz master crystal (X1) by two and distributes the resulting clock around the board and to the expansion connector.<ref name="sm" /> Because the ZX8301 steals memory cycles to fetch the display, and the 68008's data bus is only 8 bits wide, the QL performs well below what its nominal clock speed suggests.<ref name="wp" />

The 8049 was a late addition: the ZX8302 was originally intended to absorb its functions.<ref name="wp" />